NGUYN UYN

K thut a m o i t r a r i g

NH XUT BN XY DNG

NGUYN UYN

K THUT A MI TRUNG

NH XUT BN XY DNGH NI - 2004

LI GII THIU

Troni /lin nm gn dy, cng vi s lng dn s' l cc pht trin nh v bo v cng mhip, phi trin th, s dng cc ngun nng Kg, ti nguyn khc nhau. S pt trin mt lnh vc ny c tc dng dn cc lnh vc khc, ii qu ca s pht ritt dn s v kinh t dng bo ng l cc cht thi to ra qu ln, thn khng x hoc x l cha ni mc d gy ra s nhim mi (rng snh thi, nh hng ln n sc khoe cn f>i.

bo v mi trng trc tnh trng nhim d, mt ngnh khoa hc mi ra i d l K thut a mi trng - ngnh khoa hc ny s dng tng hp cc kin hc ca cc nnh khoa hc truvn lling c nh a cht, a cht cng trnh, k thut mi

, trng, ho k hui, hu cng, qun / tiiUn nc... (bi v ch ring tng ngnh khoa hc d khnq th p ng c). K thut a mi trng ! ngnh khoa hc nghin ciht 1 c cc yu t lin quan 'n cc vn mi trng mt t, cng nh di t, cng nh cc ii php k th khng ch nhim thch hp. N p dng cc nguyn l khoa hc v k thut phn tch s hnh thnh cc cht nhim, s vn chuyn ca nc, cht nhim v nn ng qua ci mi trng, thit k v thc hin cc d n x l, ci lo, s dng li hay hi gi cc cht thi.

Cun sch dc dng ging dy bc i hc, trn i hc cho cc ngnh mi a nq, xy dng, a cht cng trnh - cht thi vn, khai thc m, sinh ho... v l sch ham kho cho cc nh khoa hc, k s thc hnh thuc cc ngnh nu trn. Khi s dng, ngi dc dc trang b cc kin thc i hc ca cc mn hc: ton hc, ho hc, da cht cng trnh, a cht hu vn, c hc t, qun l cht (hi.

Nguyn Uyn Trng i hc Thu li H Ni

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M

0.1. KHI NIM V H SINH THI, MI TRNG

0.1.1. H sinh thi

Sinh vt v th gii v sinh xung quanh c quan h khng kht vi nhau v thng xuyn c tc ng qua li, c c trng bng nhng dng nng ng to nn cu trc dinh dng xc nh. S a dng v loi v chu trnh tun hon vt cht (trao i cht gia cc phn t hu sinh v v sinh) trong mt h thng, c gi l h sinh thi. Khoa hc nghin cu v mi quan h gia sinh vt v mi trng sng ca chng v gia chng vi nhau gi l sinh thi hc.

V mt c cu, h sinh thi c 6 thnh phn chia thnh hai nhm nh sau:a) Thnh phn v sinh: gm cc cht v c (C, N, C 0 2, H20 , 0 2...) tham gia vo chu

trnh tun hon vt cht, cc cht hu c (protein, gluxit, lipit, mn...), ch kh hu (nhit , nh sng, m v cc yu t vt l khc...).

b) Thnh phn hii sinh: gm cc sinh vt sn xut (sinh vt t dng, ch yu l cy xanh), sinh vt ln tiu th hoc sinh vt n snh vt, sinh vt b tiu th hoc cc sinh vt hoi sinh (vi khun, nra...)-

Trong h sinh thi thng xuyn c vng tun hon vt cht i t mi trng ngoi vo c Ih sinh vl, t sinh vt ny sang sinh vt khc, ri li t sinh vt ra mi trng ngoi. Vng tun hon ny c gi l vng sinh a ho. C v s vng tun hon v cht. Do nhu cu tn ti v pht trin, sinh vt cn ti khong 40 nguyn l khc nhau xy dng nn nguyn sinh cht cho bn thn mnh. Dng nng lng xy ra ng thi vi vng tun hon vt cht h sinh thi. Nng lng cung cp cho hot ng ca tt c cc h sinh thi Irn qu t l ngun nng lng mt tri.

Cc thnh phn ca h sinh thi lun lun b tc ng ca cc yu t mi trng, c gi l cc yu t sinh thi. Yu t sinh thi gm 3 loi:

- Yu t v sinh nh nhil , m, nh sng, p sut kh quyn... to nn iu kin sng cho vi sinh vt v nh hng trc tip n s tn ti v pht trin ca chng.

- Yu t sinh vt c trng bng cc dng quan h hoc tc ng qua li ca cc sinh vt: quan h cng sinh, k sinh hoc i khng.

- Yu t nhn to l cc hot ng ca con ngi: cng nghip, nng nghip, giao thng... ging nh mt yu t' a l, tc ng trc tip ti hot ng sng ca sinh vt hay lm thay i iu kin sng ca chng.

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Cn bng sinh Ihi l trng thi n nh trong cc thnh phn sinh tlii iu kin cn bng lng i v cu trc ton h khng b thay i. Di tc ng ca cc vu t sinh thi, mc n nh ny c th b bin i.

Cc h sinh thi t nhin u c kh nng t iu chnh ring, l kh nng thch nghi khi b nh hng ca mt VCU t sinh thi no d dc phc hi tr li trng thi ban du. l trng thi cn bng ng. Nh s t iu chnh m cc h sinh thi t nhin gi c n nh mi khi chu tc dng ca nhn t ngoi cnh.

o nhim l hin lng do hoi ng ca con ngi dn n s thav i cc yu l sinh (hi ra ngoi gii hn sinh thi ca c th, qun th v qun x... Con ngi gy nn nhiu loi nhim (ho hc, vt l, sinh hc) cho cc loi sinh vt (k c con ngi). Mun kiem sot c nhim mi trng cn phi bit c gii hn sinh thi ca c th, qun th v qun x i vi tng yu l sinh thi. X l nhim c ngha l a cc yu t sinh thi tr v gii hn sinh thi d xc nh. Mun x l tt cn phi bit cu trc v chc nng ca h sinh thi, nguyn nhn lm cho cc yu t sinh thi vt ra ngoi gii hn thch ng. l nguyn l sinh thi c bn c vn dng vo vic bo v mi trng v s dng hp l ti nguvn thin nhin.

0.1.2. Mi trng

Mi trng l tp hp tt c cc thnh phn ca Ih gii vt cht bao quanh c kh nng tc ng n s tn ti v pht trin ca mi sinh vt. Mi trng sng ca con ngi - mi trng nhn vn l lng hp cc iu kin vt l, ho hc, kinh t, x hi hao quanh v c anh hng n s sng v pht tricn ca tng c nhn v ca nhng cng ng con ngi. Mi trng sng ca con ngi l c v Ir bao la, trong c h mt tri v qu t l h phn c nh hng trc tip v r rt nht. Trong mi trng sng ny lun lun tn ti s tng tc gia thnh phn v sinh v hu sinh.

Cc quyn c lin quan n mi trng sng ca qu t gm c:- Thcl quyn (v qu t): c dy trung bnh 35km. Thnh phn ho hc, tnh

chl vt l ca thch quyn tng i n nh v nh hng ln n s sng trn qu t.

- Tlur' quyn (quyn nc): bao gm i dng, sng, h, sui, nc di t... Thu quyn ng vai tr khng th thiu dc trong vic duy tr cuc sng con ngi, sinh vt v cn bng kh hu ton cu.

- Kh qitxn: lp khng kh tng i lu bao quanh qu t. Kh quvn ng vai tr cc k quan Irng trong vic duy tr s sng v quyt nh tnh cht kh hu, thi tit lon qu l.

- Sinh quyn: ni sinh sng ca cc sinh vt, thng lp trn cng ca thch quvn. trong thu quyn.

Theo mc ch v ni dung nghin cu, mi trng sng ca con ngi c chia thnh:

b

- Mi trn Ihin nhin: bao gm cc nhn t t nhin: vt l, ho hc, sinh hc, tn ti khch quan ngoi mun ca con ngi, hoc t chu s chi phi ca con ngi.

- Mi trng x hi: bao gm cc mi quan h gia ngi v ngi.

- Mi rn nhn to: bao gm nhng nhn t' vt l, sinh hc, x hi do con ngi to nn v chu chi phi ca con ngi.

Ba loi mi trng ny tn ti cng nhau, xen ln vo nhau v tng tc ch ch.

0.2. CC TC NG CA CON NGUI i VI MI TRNG

Cc hot ng chnh lm nhim bn v gy tc hi i vi mi trng c th c phn ra nh sau:

0.2.1. Khai thc ti nguyn

Vic khai thc g v cc loi sinh vt ca rng dn n vic tn ph rng, thay i cu Irc thm thc vt trn hnh tinh. Hu qu dn h thay i ch v chu trnh cht kh, hm lng C 0 2 tng v 0 2 gim, nhit khng kh cng c xu hng tng theo, hin tng xi mn v cun tri t lm mu m ca t rng b gim, nc ngun b nhim bn ph sa, ch dng chy ca sng ngi thay i...

Cc ngnh cng nghip khai khong, khai thc du m... a mt lng ln ph (hi, cc chl c hi... t lng t vo sinh quyn. Do khai thc du v vn chuyn du, mi nm c hng triu tn du vo i dng. Cc loi nc cha axit, phenol... ca qu trnh khai m x vo ngun nc mt, gy nhim v ph hu cn bn sinh thi trong .

0.2.2. S dng ho cht

Con ngi s dng mt lng ln ho cht trong cc hot ng kinh t x hi ca mnh. Trong nng nghip s dng phn ho hc vi mc ch canh tc, tng nng sut cy trng nhng mt tri ca n l lm nhim t do khng trong sch v lm nhim ngun nc do tng ph dng bi cc nguyn t N, p...

Cc thuc tr su v dit c l cc cht bn vng d b hp th vo cu t ca t, ph hu cy trng v xm nhp vo chui dinh dung, cn tr hot ng sng ca nhiu sinh vt.

Cc ho cht s dng trong cng nghip v cc hot ng kinh t khc thot vo mi trng di dng ph thi. Cc cht nh xianua, ch, ng, Ihu ngn, phenol... l nhng cht c hi i vi con ngi v cc loi sinh vt khc.

Cc cht phng x do n bom ht nhn hoc nhng cht thi phng x tng hay rn t cc trung tm cng nghip hay nghin cu khoa hc, c the lng xung t, tch t d hoc lan truyn trong khng kh, c th gy nguy c dc hi i vi con ngi, ng vt v thc vt.

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0.2.3. S dng nhicn liu

Trong hot ng sng cua mnh, con ngi s dng nhiu loi nhin liu khc nhau: than , u m, kh t, ci... t nhin liu c xem nhu s t nng trc tip sinh quyn, nhng nguy hi l hm lng C 0 2, SO-,... trong kh quyn tng ln. Mt ngun ln .sn snh SO-> l t chy than (67%), du m (12%)... l nguyn nhn ca ma axit, lm chua ho thin nhin.

0.2.4. th ho

Mt lng ln rc thi, ph thi sinh hot v cng nghip tp trung trong t, lm nhim bn t v nc ngm, nc mt, nh hng n tnh trng v sinh th. nhim ngun nc sng h v nc ngm do cc loi nc thi sinh hot thnh ph v nc thi cng nghip l nghim trng nht.

Vic xy dng cc cng trnh, nh cao tng trn nn t, khai thc nc ngm hoc khai khong lm cho b mt t b bin dng, xut hin khu vc m ly... Thnh ph lm thav i hon ton cc thng s dng chy v d ngm ca nc ma. H -S thm nc gim r rl do ph bin rng ri lp ph khng thm (ng s, mi nh...), t h thng cng ngm...

0.3. THC TRNG NHIM MI TRUNG T V NUC VIT NAM

0.3.1. Mi trng t

Hin Vit Nam vn cn 8 triu 65 ha t trng, i trc trong c khong 7,5 triu ha c th pht trin nng nghip v trng trt. Nguyn nhn l do tnh trng cht ph rng ba bi, h thng qun l ring cha ph hp...

cc vng khai thc m u thiu k hoch hon nguycn mi trng v x l t khai thc nn ph hoi mi trng t gy hin tng xi l, bi lng trn phm vi ln. Khai thc than gy ph a tng, a mo, lp ph thc vt, thi ra cc cht nhim th rn, th lng v phng x vo t. Khai thc du kh cng thi ra nhiu dung dch khoan v mn gy nhim mi trng bin.

t trng trt chim 22,2% din tch t nhin ang b bc mu, nhim mn, nhim ca nc thi, nc rc thm ngm lm ny sinh nhiu vi khun, su bnh ph hoi cy trng.

0.3.2. Mi trng nc

Nc bin ven b b nhim t t lin ra, c c s c trn du v nhim t cc ng thi bin xa n, hu qu lm suy gim ngun ging v ngun [i thu sn...

Nc sng ngi b nhim cc cht hu c, mt s sng c du hiu nhim km loi l do s dng phn bn, lm dng thuc bo v thc vt, cc lng ngh pht irin nng thn, cc x nghip cn dng cc cng ngh lc hu (Lng ng Bc Ninh

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thi hng ngn m'1 c cht ty vi nng NH3, PH cao; lng Vinh Lc H Ty thi 20.0001 nc/ngy c g .st thcp v nc m c ZnS04, FeS04...)-

Ti l dn c cp nc my mi ch t 70%, mi trng nc mt b nhim nng nn nc ngm c chi liu cao hn so vi tr s tiu chun 10 ln.

Nc thi ngy cng lm nhim mi trng t v nc t nhin nht l cc thnh ph, khu dn c tng ln. Nc r r t cc bi rc, ngha trang chua c x l theo cng ngh tin tin nn cn nhiu c t thm vo t v ngun nc ngm..

X l rc thnh mi quan tm c bit nht l th v khu dn c vi khi lng kh ln (H Ni 1300 tn/ngy), song bin php hin nay mi ch l thu gom ri bi t nhin, khng ncn p nn rt tn din tch cha, li khng chc ph nn gy nhim ngun nc ngm rt trm trng.

Nc thi sinh hot, thi bnh vin... cc dng, h thng ng cng, ga thu a s kch thc, c khng cn thch hp vi lng nc thi khi th pht trin ncn hin tng ng, ngp ng mi kh ma ln thng xy ra.

Nc thi cng nghip l cc c s sn xut c c hi nh ho cht v kim loi nng gy hu qu nghim trng v vic x l rt kh khn. Ngoi khu cng nghip cao v 3 khu ch xut, a s x nghip u c quy trnh sn xut v thit b c, lc hu, trnh d thp gy nhim nng cho mi trng nh cng nghip nng (khai khong, ho cht, phn bn, luyn kim), cng ngh truyn thng (giy, dt may, da giy, nhum, ch hicn nng sn thc phm). Cc lng ngh pht trin nhiu (H Ni 40, H Ty 88, Bc Ninh 58, Hng Yn 24, Nam nh 71...), nhng c ti 90% cha qua cc trng o to, hu ht sn xut theo kinh nghim cng l nguyn nhn ng k gy nhim.

Vit Nam c nhiu sng, h, kcnh mng thun li cho vic t lm sch v iu chnh nc thi, song vic no vt cc lng sng, h thnh ph cha thc hin thng xuyn nn ct y sng b cao l 0,5 - lm, cn y h qu ln lm gim kh nng iu ho v thot nc ton h thng.

Nguyn nhn nhim ch yu do cc cht hu c tn dng, gii php hu hiu l x l ti cc ngun thi v no vt lng sng, h, knh mng cho lu thng dng chy, cng ho knh mng. X l nc thi cng nghip bng vi sinh, nc thi bnh vin bng phng php phn hu sinh hc k kh v m c nh. Xy dng nh my x l rc. Nui cc loi c bng ngun nc thi tp trung vo ao h tiu th cc cht hu c, nui trng to, bo hoa du v cc ch phm sinh hc l mt s sinh vt c kh nng c nh m d lm sch nc bn hu c thm vo t... Trn y l mt s gii php x l mi trng b nhim c tin hnh nc ta.

bo v mi trng t v nc trong thi gian ti t kt qu tt, chng ta phi c chin lc bo v mi trng tng ng vi chin lc pht trin kinh t x hi mt cch bn vng, mt khc phi c gii php v th ch, chnh sch, t chc qn l, phng

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nga (ti u ho qu trnh sn xut, i mi s dng cng ngh tin tin s loi tr cc yu t c hi v gim ti thiu khi lng cht thi...), nng cao nhn thc v bo v mi trng trong cng ng x hi ton dn tham gia thc hin.

0.4. N DUNG V CC PHNG PHP NH GI TC NG MI TRNG

0.4.1. Ni dung nh gi tc ng mi trng

- M t a bn ni s tin hnh hot ng pht trin, c im kinh t k thut ca hot ng pht tricn.

- Xc nh phm vi nh gi.

- M t hin trng mi trng a bn c nh gi.

- D bo nhng thay di v mi trng c th xy ra trong v sau khi thc hin cc hot ng pht trin.

- Cc gii php phng trnh, iu chnh.

- Kt lun v kin ngh.

0.4.2. Cc phng php nh gi

thc hin cc ni dung nh gi tc ng mi trng, thng dng cc phng php nh gi sau y :

a) Phng php tii k cc s liu v thng s' mi trng

Chn mt s thng s lin quan n mi trng, lit k ra v cho cc s liu lin quan n cc thng s , chuyn ti ngi ra quyt nh xem xt m khng phn lch, ph phn g thm.

Phng php ny s lc, n gin tuy nhin rt cn thit v c ch trong bc nh gi s b v tc ng n mi trng.

b) Phng php danh mc cc iu kin mi trng

Lit k mt danh mc tt c cc nhn t mi trng lin quan n hot ng pht trin c em ra nh gi. Danh mc c cc chuyn gia nh gi theo thang im. Tng tc ng E ca mt hot ng pht trin n mi trng c xc nh theo:

m m

i = i = l

Trong : m - s nhn t mi trng;

V, ] ' t r s nhn t mi trng lc n c thc hin v hot ng;

V 2 - tr s cht lng mi trng Lc cha thc hin n;

Wj - tm quan trng ca thng s mi trng tnh theo im quy c.

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y l phng php r rng, d hiu. Tuy nhin phng php ny mang tnh cht ch quan ca chuyn gia, cc danh mc chung chung, khng y .

c) Phri php ma trn mi trng

Lit kc cc hnh ng ca hot dng pht trin cng nhng nhn t mi trng c th b tc ng vo mt ma trn. Cch lm ny cho php xem xt cc quan h nhn - qu ca nhng tc ng khc nhau mt cch ng thi.

Phng php ma Irn tng i n gin, c s dng kh ph bin, khng i hi qu nhiu s liu v mi trng, sinh thi cho php phn tch mt cch tng minh tc ng ca nhiu hnh ng khc nhau ln cng ml nhn t. Tuy nhin phng php ny c nhc dim l cha xt cc tng tc qua li gia cc tc ng vi nhau, cha xct tiin bin theo thi gian ca tc ng, cha phn bit c tc ng lu di vi tc ng tm ihi, vic xc nh tm quan trng ca nhn t mi trng, ch tiu cht lng mi trng cn mang tnh ch quan...

d) Phng php m hnh

M hnh cho php d bo cc din bih c th xy ra ca mi trng, la chn dc cc chin thul v cc phng n khc nhau a mi trng v trng thi ti u v d on tnh trng ca mi trng ti nhng thi im, nhng iu kin khc nhau ca hot ng.

Phng php ny cn c s dng rng ri quy hoch v qun L mi trng. Phng php ny i hi kinh ph cao, nhiu ti liu o c v mi trng, nhiu chuyn gia lin ngnh cng tham gia. Vi s pht trin ca tin hc, kh nhiu m hnh my tnh ra i v phc v cho vic nh gi v s nhim ca mi trng.

M hnh Konikow r Bredehofi (MOC) (Konikow & Bredehoft, 1978) l mt m hnh vn chuyn cht ho tan da trn mt kiu sai phn hu hn v dng phng php c c trung cho cht ho tan. N l m hnh hai hng v lnh c cc thay i ca nng theo thi gian gy ra do tc dng mang theo, khuch tn thu ng v hn hp. M hnh MOC c ci tin a vo tc dng phn hu phng x, ht thm cn bng v trao i ion.

M hnh vn chuyn bo ho - khn bo hu (Saturated - Unsaturated Transport - SUTRA) (Voss, 1984) l m hnh m phng phn t hu hn cho s chuyn ng ca cht lng v s vn chuvn cc cht ho tan do phn hu, hoc s vn chuyn nng lng di cc iu kin bo ho v khng bo ho. Trong kiu vn chuyn cht ho tan, cht ho tan c th b hp ph vo mi trng rng cng nh b phn hu hay sn sinh. Ngoi ra n c the m phng dng cht lng c trng lng ring bin i nh nc bin hay nc ra la.

RNDWALK m hnh v vn chuyn cht ho tan (PrickeU, Naymik & Longquist, 1981). i m hnh ln theo du vt ht, trong chng trnh my tnh s chuyn cc

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ht biu th cht nhim theo phng ngang ri sau khuch tn chng theo mt phn b' chun xt n s khuch tn.

ERMA GROUNDWATER MODELER l m hnh qun l ti nguyn mi trng ca hng Intergraph bao gm ba b phn mm: Modflow, Modpath v MT3D. Modflow c s dng xc nh vn ng ca dng ngm; Modpath dng xc nh cc cht nhim vn ng qua din tch nghin cu v d on thi gian cht nhim di chuyn ti im cn nghin cu, MT3D dng xc nh s vn ng i lu, s phn tn ca vt cht v cc phn ng ho hc din ra trong nc ngm.

BOWAM l phn mm ca m hnh v trng thi ca nc trong th nhng, trong ni dung ch yu l m hnh ho cc qu trnh th vn xy ra trong i thng kh (qu trnh thm v ngm, dch chuyn hai m, bc hi...).

CTRAN/W l phn mm phn t hu hn dng m hnh ho s di chuyn cht nhicm. CTRAN/W c th ng phn tch cc bi ton n gin nh theo di cc ht di chuyn do nc vn dng cho ti cc vn phc tp lin quan cc qu trnh khuch tn, phn tn, hp ph v phn hu phng x. CTRAN/W nm trong phn mm GEO- SLOPE do Cng ty a k thut quc t GO-SLOP International phi hnh nm 1997, hin ang c s dng rng ri nc ta cng nh nhiu nc trn th' gii (M, Canada...)

e) Phng php phn tch li ch chi ph m rng

Phng php ny s dng cc kt qu phn tch, nh gi v tc ng mi trng m cc phng php nu trn a li. T i su v mt kinh t, tin thm mt bc so snh nhng li ch m vic thc hin hot ng SC em li, vi nhng chi ph v ln tht m vic thc hin hot ng s gy ra.

Phng php ny thch hp cc nc ang pht trin. y l nhng phng php ng n v c s la chn cui cng l cc thng s kinh t. Hn ch ca phng php ny l khng th xt tt c cc nh gi tc ng mi trng, nht l cc lc ng mang lnh lu di hoc gin tip. Vic s ng phng php ny vo cc d n ln c kh khn do s hng mc cn phn tch v tnh ton qu ln.

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Phn 1

CC TUNG TC CO L - HO V SINH HC TRONG DT

Chng 1

S THNH TO V CC THNH PHN CA T

1.1. STHNH TO DAT

t c hnh thnh do s phn hu (hoc chnh xc hn l s ticn ho) ca cc cu to nn v qu t. S n nh ca kin trc kt tinh khng ch s thnh to . Khi nhit h thp, cc khong vt mi, n nh hn c hnh thnh. V d, mt trong cc khong vt ph bin nht l thch anh c c kin trc kt tinh n nh khi nhit h thp di 573c. Cc khong vt trung gian v km n nh th d phn hu trong qu trnh hnh thnh to t.

Qu trnh phong ho phn hu thnh t: xy ra do cc yu t t nhin, trong ch yu l gi v nc. Cc qu trnh phong ho gm c:

1. Xi mn do cc lc ca gi, nc hay bng h, v do s xen k gia thi k ng bng v tan bng ca vt liu .

2. Cc qu trnh ho hc thng dc kch thch do s c mt ca nc.

Cc qu trnh ny bao gm: a) Thu phn (phn ng gia cc ion H+ v OH ca nc v cc ion ca cc khong vt ); b) Phc hp v loai b cc ion kim loi;c) Trao i cation gia b mt khong vt ca d v mi trng xung quanh; d) Cc phn ng oxi ho v kh; e) S cacbon ho b mt khong vt do C 0 2 c trong kh quyn.

3. Cc qua'trlnh sinh hc do cc hp cht hu c nh hng trc tip hay gin tip n qu trnh phong ho.

Mt khi b phong ho th t to thnh c th gi ti ch hay c nc, gi hay bng h vn chuyn i. Loi dt nm nguyn ti ch gi l trm tch, cn t c vn chuyn c th l bi tch, gi tch hay bng tch. Da trn iu kin vn chyn v trm ng c th chia ra cc nhm ch yu sa y:

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1. Trm tch sng phn nhnh thnh to dc theo lng sng do s trm dng t cc sng qu t. S phn nhnh gm c s ln cc lng sng nh c chia tch bi cc o.

2. Trm lch di un cong hnh thnh do sng un cong v t b lm b xi l v b li c trm ng.

3. Trm tch h hnh thnh o vt liu trm ng trong cc h di tc dng ca trng lc.

4. Trm tch bin hnh thnh do s trm ng cc ht bin.

5. St tn^ do bng hnh thnh do s trm ng cc ht khi bng h lan v t bi tch- bng hnh thnh do cc lng sng (tng t trm tch dng phn nhnh) c tao do bng tan.

6. Trm tch h bng hnh thnh khi nc bng tan mang theo cc ht nh to nn cch v cc hl lng chm trong h.

7. Ct gi tch hnh thnh cc n ct v t hong th to thnh khi cc ht nh hn l ct gi tch v tn ti thnh cc lp mng.

8. t l tch hnh thnh ti ch thp sn i do t di chuyn xung di tc dng trng lc v s mt n nh ca sn i.

Cc tnh cht ca trm tch t ph thuc vo cc yu t ch yu quyt nh s hnh thnh t, l: kh hu, vt cht hu c, a hnh, bn cht ca gc v thi gian.

Thnh phn ca t uc quyt nh bi qu trnh phong ho v do cc qu trnh vn chuyn v rm ng sau . t ng ng thnh lp v mi lp c tnh cht ring phn nh thnh phn gc sn sinh ra n. Cc yu t mi trng nh kh hu, dc a hnh, s c mt ca vt cht hu c cng quyt nh c tnh ca mi lp. Thnh phn t ca cc lp khc nhau thng c m t bng mt ct th nhng. Mi lp c gi l mt tng. Cc tng c k hiu bng cc ch vit hoa o , c , A, B v E.

Trnh t ihnh to cc lp dng s c thy hnh 1.1. N bt u bng tng c biu th gc l ra, c th b bin i nh do cc yu t kh quyn. Sinh vt v cy ci bt u chim lnh b mt tng c , to ra mt lp bao gm ch yu l vt chl hu c. Khi iu kin kh quyn khng thch hp phn hu (chng hn thiu oxy), vt cht hu c c th c mt lp trn cng nh cc trm ng than bn v t m ly. N hnh thnh tng o c biu l bng vt cht hu c khng phn hu hay phn hu mt phn. Theo thi gian vt cht hu c b tiu ho v phn hu bi ng vt v vi khun to ra mn c sc khng tng i vi s bin i thm na. Lp cha vt cht hu c ho mn hnh thnh tng A. Cc qu trnh phong ho tip tc to nn cc ht nh loi st, cc ht ny c nc ngm d chuyn xung di qua tng A. Cc ht mn ny c gi lu di su trung gian gia tng A v c , hnh thnh tng B. Qu trnh ra sch cc ht t tng A v cng nh th trong tng B i khi c xem l s loi st khit v s tch t bn (tch t iluvi).

14

gc

V///,IPmm

ppW/.

g mgc

gcc.

I

1 2 /.. Bgc

Hnh 1.1: Trnh t thnh to cc lp trong mt ct th nhng

S thnh to tng B din ra hng ngn nm. Hnh 1.2 cho thy qu trnh ko di ny ca granit b phong ho thung lng trung tm ca California. thnh to tng B phi mt 140.000 nm vi lng st gp 3 ln lng st ca tng A. Trong mt s trng hp qu trnh loi st khi t ko di c th mnh li ti phn y tng A ton b cc hl mn ra sch to ra tng E (tng loi st ton b khi t).

S thnh phn t do th nhng hc nghin cu l s hu ch nghin cu cc c trng ca t gn mt t i vi cc yu t thnh to. S tho lun chi tit hn v th nhng c thy trong cc sch gio khoa ca Mcre (1988), Forth (1990) v Lyon et al. (1952). Tuy nhin, cc nghin cu th nhng ch nh tnh v bn cht v chng c s dng hn ch trong nghin cu cc c trng c hc v k thut ca l.

Phn trm st 10 20 0 10 20 0___10 20 30 0 10 20 30 40

Nm 1000 10.000 100.000t Han ford Greenfield Spelling

140.000 San Joaquin

Hnh 1.2: Thnh to dn dn tng B bao gm st l granit thung lng Trung tm ca California

] .2. CC THNH PHN CA T

1.2.1. Cc thnh phn ca t

Trong qu trnh thnh to, do s tng tc gia gc, cc nhn t kh quyn (ch yu l nc v khng kh) v vt cht hu c nn t ch yu bao gm bn thnh phn

15

hay bn pha sau: vt cht khong, vt cht hu c. nc v khng kh. Trong nghin cu v cc tnh cht ca t, cn bit t l tng i ca cc thnh phn ny.

Thnh phn th tch in hnh bn pha ca t c thy trong hnh 1.3. Trong bn thnh phn, vt cht hu c chim th tch nh nht v gim dn theo chiu su t mt l. Ni chung, lng vt cht hu c bin i mnh t ni ny n ni khc v eng c th thay i ln ngay trong mt vng. Tuy nhin nh thy hnh 1.4. m t bn mt ct th nhng khc nhau, lng vt cht hu c gim nhanh theo su. Ni chung, s Ihot nc km lm lng cao vt cht hu c trong cc tng trn mt. Khi nghin cu a k thut thng b qua vt chl hu c trong thnh phn pha ch yu l do n ch nh hng gii hn ti cc lp trn mt. Tuy nhin, n ng vai tr quan trng trong k thut a mi trng.

Phn trm vt cht hu c

Hnh 1.3: Thnh phn th tch in hnhca bn thnh phn trong t ini 1 4 ; Bin i vt cht hu c

(! l nc v khng kh bin i mnh) ifie0 su

T l tng i nc v khng kh ng vai* tr quan trng trong thc tin k thut. Trong mt khi t cho, cc pha nv u bin i theo khng gian v thi gian. T l tng di cc pha lng ny khng ch phm vi quyt nh n kh nng vn chuyn cht nhim ca t. Hai pha lin tc tng tc vi pha rn v tham gia vo s trao di qua' li cc cht nhim. Di y chng ta s nh ngha cc thut ng c dng biu th s nh ng t l tng i ca cc pha rn, nc v khng kh. Tng ng vi thc tin chung, chng ta khng phn bit vt cht khong v vt cht hu c trong pha rn. Hnh 1.5 cho thy s biu th ba pha tng ng theo trng lng (pha bn tri) v th tch (pha bn phi).

Cc ch s th tch c bn thnh phn pha gm c:

16

H s rn e - t s ca th lch khong rng (do nc v khng kh chim ch) vi th tch pha rn:

V,.e -

V,( 1- 1)

rng n - t s the tch khong rng vi th tch tng ca khi dt:

w

n =V

( 1-2)

bao ho s - t s th tch nc vi th tch khong rng:

V.S = - ^

V.,(1 -3 )

w-------------Nc ---- ------------

Khng khi

Ht 'n

m th tch 0 - t s th tch nc vi th lch lng khi t:

0 =

Hnh 1.5: S biu ill cc pha rn, nc v khng kh trong t

V(1-4)

Trong bn ch s, h s rng v rng biu th mc h tch ca khong rng, bo ho v m th tch th hin m tng i ca t.

Cc ch s trng lng c bn thnh phn pha gm c:

m w - t s' trng lng nc vi trng lng pha rn:w.w = w s

Trng lng n v y - trng lng cho mi th tch n v khi t:w

Y = V

( 1 -5 )

( 1-6 )

Cn nh l m c xc nh c theo th tch [phng trnh (1-4)3 v trng lng [phng trnh (1-5)]. m th tch c dng trong thu vn v th cht, cn d m Irng lng c dng ph bin trong a k thut. Cc k s a k thut thng thy n h dng d loi tr pha rn v xc nh trng lng n v ch ring theo trng lng pha rn. Trng lng n v c gi l trng lng n v kh c cho bi

w(1-7)

Khi dng trng lng ring Gs ca pha rn (t s trng lng n v cua pha rn vi trng lng n v ca nc) v trng lng dn v ca khi t (y hay d) v nc (yw),

17

c kh nng lin h cc ch s th tch v trng lng c bn ca thnh phn pha. Vi s h tr ca hnh 1.6, c th da ra cc biu ihc sau:

n -

0 =

1 +e

Wy w

Sc = WGS

S = ^ n

( 1-8)

(1-9)

( 1- 10)

( 1- 11)

wNc ' _

Khng khi

Hat rn '

Hnh 1.6: Cc quan h pha

Y.I = 1 -W( 1- 12)

(1 - W)GsywY =

Yd =

1 + e

Gsy w1 + e

(1-13)

(1-14)

Cc biu thc trn hu ch khi nh gi ng tng i ca cc pha rn, nc v khng kh trong t.

1.2.2. Cc qu trnh a k thut khng ch thnh phn cc pha

Thnh phn cc pha ca t bin i rt ln v c khng ch hi c cc qu trnh t nhin v qu trnh nhn to. Hai qu Irnh dc ngi k s a k thut bit l c kt v nn cht. C kt l qu trnh lm gim h s rng do ti trng tc dng ln khi t hon ton bo ho nc. Nn cht lin quan vi s gim h s rng ca pha kh, thng dn ti lm tng trng lng n v kh ca khi t. Nn cht l qu trnh quan trng

Hnh 1.7: M t cc bin di trong qu trnh c'kt a ,b) v ttit cht c , d

18

irong khi thi cng p v cc cng trnh t khc, v lp t bi rc thi. Mc d c kt v nn cht c dng ng ngha trong mt s mn hc a cht v th cht, chng ta chp nhn s khc bit quan trng ny trong lon b cun sch ny. Hnh 1.7 cho thy s pha m t s khc bit gia hai qu trnh. Hai qu trnh c trnh by nhng nt chnh trong cc mc di dy. Vic m t su cc qu trnh ny ngi c c th tham kho cc chng trnh chun v c hc t hay a k thut.

Nn cht dt

Trong xy dng cc cng trnh nh nn dng, p, lp lt hay bi t thi, cn s dng kho lo t l tng i pha lng trong t. m ca t v nng lng m t c p quyt nh ln phm vi dung trng ca khi t. Nc c tc dng bi trn cc ht rn v ko chng gn nhau hn. Hogentogler (1936) gii thch iu ny bng bn giai on lm m l ngm nc, bi trn, trng n v bo ho. Trong giai on ngm nc ban u, nc c hp th bi cc ht t nh l cc mng mng dnh kt. S tng thm nc s chuyn sang giai on bi trn khi m nc tc dng nh l cht bi trn, lm cho cc ht rn sp xp li gn nhau hn. Do vy trng lng n v kh ca khi t tng ln. S tng thm nc tip s lm t b trng n vi mt lng kh cn lu gi li. Mc d khng dt c trong thc t, giai on th t bo ho c hnh dung c kh nng khi khng kh c nc thay th hon ton.

S bin i trng lng n v kh theo m ban u ca t p theo ng cong dm cht. Hai ng cong m cht khi qut dc thy trong hnh 1.8, tng ng vi hai nng lng m cht khc nhau c dng ph bin trong phng th nghim t vi ba Proctor tiu chun v ba Proctor ci tin. Ghi nh l mt khi t cho, trng lng n v kh c quan h nghch vi h s rng [phng trnh (1 -14)] nh thy trn trc V hnh 1.8. S ui hon ton khng kh khi cc l rng m p c th cho trng lng n v kh ln nht, c th c theo l thuyt. Cn nh l e = WGS lc t hon ton bo ho bi pha nc [phng trnh (1-10)], ngi ta c th nhn c dung trng kh l thuyt ln nht ymv tcmg ng vi l rng khng kh bng khng khi dng phng trnh (1-14) c dng:

y z a v - T ^ r (1-15)1 + wGs

ng biu th phng trnh (1-15) thng thy dc theo cc ng cong m cht khi ng l rng khng kh bng khng (hnh 1.18). S tng nng lng m cht s lm cho trng lng n v kh cao hn nh mong i, ty nhin thc n khng th loi b tt c l rng khng kh v t ngoi tri. S tng trng lng n v kh (hay gim h s rng) v cc bin i ct khi t km theo ng vai tr quyt nh cc c trng vn chuyn cht lng ca t m cht. iu ny lm cho qu trnh m cht

19

l rt quan trng trong lp lt ca cc cng trnh cha cht thi. S bin i kt cu t do m cht c cp chi tit trong chng 2 v s bin i cc c trng vn chuyn cht lng ca t c m cht nh l hm s ca cc bin m cht ( m t p, nng lng m cht) c cp trong chng 3.

m, w(%)

Hnh 1.8: Bin ni din hnh ca trng ng dn v kh v h s rnq do m cht

C kl ca dl

Tri ngc vi qu trnh m cht, c kt lin quan vi nc thot ra khi dt dn n h s rng gim xung. V qu trnh lin quan n s di chuyn ca nc trong t t im c p lc cao hn n im c p lc thp hn, n l qu trnh ph thuc vo thi gian. Ph thuc vo loi t, b dy lp t v d Jn cua p lc biu l trong nc l rng, qu trnh c kt c th ko di vi nm hay hng chc nm.

Gi tr h s rng tng gim i do ti trng tc dng thng c nh gi theo mu t ti ch chu gia li trong phng th nghim v nhn c quan h ng sut - bin dng. Quan h ng sut hi qu tc dng ln mu t v h s rng c thy trn hnh 1.9. ng sut hiu qu l mt chi ho ng sut gia cc ht c sinh ra hi ct t. Nguyn ng sut hiu qu ca Tcrzaghi pht biu l ng sut hiu qu l chnh gia ng st tng v p lc nc l rng. Mt khi bit dc ca ng cong c kt, c th nh gi c gim h s rng do tng ti trng cho. Ni chung, trn ng cong c kt biu hin hai dc khc bit. Vng I (hnh 1.9) hiu l s gim thp h s rng cho thy l mu t dc nn cht trong qu kh di cc ng sut tng t. Vng II biu l s gim h s rng qu ln th hin mu t ang chu cc ng sut thi gian u. Hai vng gp li p c c kt trc p

20

bit, l ch s bo p lc ln nht mu t d chu trong qu kh. Thng s ny cho bit lch s ng sut lp ph ti hin trng t ni nhn c mu t th nghim trong phng. Vng c 'k t ihng ting khi p lc lp ph hin thi p0 bng pc v qu c kt khi p0 < p .^

Hnh 1.9:S gim h so rung (rang qu trnh c kt

Theo dc ca dng cong c kt (ch s nn) v Cs (ch s n) c th nhn c gi tr h s rng bin i Ae cho gi tr gia ti trng p cho:

Ae - Cc lg pc + p''1

Ae = c s Ig

Po

Pc + AP

cho t st c kt thng thng

cho t st qu c kt, khi p0 + p < pc

( 1- 16)

(1-17)-0 /

Ae = c s lg 'PL + Cc lg 'Pc + AP^,p ny ^ Po )

cho t st qu c kt, khi pu + Ap > pc (1-18)

Tc h s rng gim theo thi gian trong qu trnh c kt chu khng ch bi loi phng trnh trycn nhit. iu ny c cp trong chng 3 nh l mt trng hp c bit ca dng nc ngm.

1.3. THNH PHN PHA RN V C TRUNG CA N

By gi chng ta gii hn trng tm vo pha rn v nghin cu thnh phn ca n trong thin nhicn v kch c ca cc ht rn. Nu r kch c cc ht l mt trong cc cch c trng pha rn. Tuy nhin, do bn cht ca qu trnh phong ho, kch c cc ht rn bt gp trong khi t bin i rt ln. Hnh 1.10 m t phm vi kch c cc ht

21

c nhm li di cc loi ph bin: ct, bi v st. S khc nhau t nht 100 ln gia kch c ht ct v ht st. S tn ti ng thi cc ht c phm vi kch c rng ny r rng to ra kin trc khong rng khc nhau trong t v v th s nghin cu kt cu rng trong chng 2 l quan trng.

C(

Hnh .l : Kch c tng i cc ht, cc nhm ht ct, bi V st

Kch c cc ht l c s chia nhm cc ht rn thnh ct, bi v st. Mt s nhm ht c pht trin trong nhiu nm bi cc t chc khc nhau. Hnh 1.11 cho thy cc nhm ht ngh bi cc t chc ch yu. C h! m ch ng knh hnh cu tng ng, cng ph bin c trng pha rn thnh mt s nhm ph khi dng tam gic cu to (hnh 1.12).

ng knh ht (t l Ig) (mm)

0.001TTT

0.01 I m i l

0.1TT-rTTTrp-

1.0TT!rT-nrrp 10.0 r T T T

ISSS St

I

St I Bi

I

Rtmin Mn Truog Th | i l I1* 1 si

Ct I

I I Min ThSt I Bui I------- -----------------1 Si

I I Ct 11T

USPRA St ** I Bi

BSIMIT

' St

DIN St

Mn .___ Th

Ct

Bi Ct

BiCt

Si

Si

Si

Hnh . i l : Cc nhm ht t da trn ng knh it ca cc t chc khc nhau USD A - B Nng nghip M; SSS - Hi Th cht quc t;USPRA - V hnh c It till ng cng cng M; DN - Tiu chun c;BS - Vin Tiu chun Anh v MT - Vin k thut Massachusetts).

22

100 90 80 70 60 50 40 30 20 10

Phn trm trng lng ct

Hnh 1.12: Phn loi kt cu dt

Vic xc nh thc nghim kch c ht bng cch ry c hc cho cc ht ln hn0,075mm v phn tch binh t trng cho cc ht nh hn 0,075mm. Ry c hc s dng cc ry bit kch c li xc nh phn cc ht rn qua mi ry. Phn tch bnh t trng da trn nguyn l lng ng ca cc ht t trong nc. Dng nh lut Stoke lin h ng knh D ca ht (gi thit l hnh cu) vi vn tc lng ng v:

Trong phng th nghim, dng t trng k gim st lng ht t th vn ti cc thi gian khc nhau. Lng cc ht th vn tng ng cc ht c ng knh D c d on bng phng trnh (1-19).

Bng cc phn tch ry c hc v t trng k, phn tch lu Fj ca cc ht mn hn ng knh tng ng D[ ring bit c th xc nh theo:

18r|

Trong : Ys - trng lng n v cc ht rn;

Yw - trng lng dn v nc;

T| - nht ca nc.

(1-19)

( 1-20)

23

Trong : EW| - trng lng tch lu ca cc ht mn hn kch c th i; w s - tng trng lng cht rn.

C th thnh lp s phn b kch c ca cc ht rn bng cch v Fj i vi kch c ht nh hnh 1.13. Da trn s phn b kch c ht thng dng hai thng s sau y so snh cc t khc nhau.

H s'ng nht (1-21)

D2H s cp phi Cp = (1-22)

g D6o x D 10

Trong : D 10, D30 v D60 l ng knh ht tng ng vi 10%, 30% v 60% mn hn. D |0 cn gi l kch c hiu qu ca pha rn.

ng tnh ht (mm)

Hnh .13: S phn b c hi ii hnh ca t S c trng thng khng thch hp cho trng hp dt st. Khng ging ct v

bi, t set hot ng ho hc v tin hnh cc phn ng vi nc. Hai oi st khc nhau c th cng cha cc ht c cng phm vi kch thc nhng phn ng rt khc nhau vi nc. Chng cn lng nc khc nhau c cng c. Khi m nh, l st c hnh vi nh th rn. Khi m tng ln, chng t giai on na rn v do cho ti giai on m pha nc lm cho pha rn hnh vi ging nh cht lng. Cc giai on ny c Atterberg nh ngha chnh thc vo cc nm u 1900 v nay c gi l cc gii hn Atterberg. Cc thc nghim n gin c tin hnh theo th t quy nh trong cc phng th nghim c hc t xc nh m, ti t st tri qua ton b cc giai on khc nhau. Ba gii hn thng dng c trng cho t st l:

. Gii hn co ngt: l m ti t t trng thi rn sang na rn.2. Gii hn do: l m ti dt chuyn t trng thi na rn sang trng thi do.3. Gii hn chy: l m cn t st bt u biu hin cc c trng ng chy

nh cc cht lng.

24

Vi cc phng php n gin xc nh cc gii hn st ny ngi c c th tham kho cc sch gio khoa hay s tay th nghim a k thut trong phng. Ni chung, cc gii hn Atterberg c tha nhn l cc ch bo hu ch cho hnh vi k thut cua t. Mt s tnh cht k thut irong a k Ihut lin quan vi cc gii hn ny. m ti d t st chuyn t trng thi ny sang trng thi khc, biu hin ton b bn cht l - ho ca chng. Ring gii hn chy c thit lp gn y l trng thi ti nhiu khong vt st khc nhau li c nhng tnh cht nh nhau. Khi chng ta xem xt trong mc sau, cc khong vt khc nhau cn lng nc khc nhau a chng ti trng thi gii hn chy. Tuy nhin, mt khi chng trng thi gii hn chy, tt c cc t khc nhau ln dng nh li c mt nhm cc tnh cht k thut tng i c nh, chng hn nh ht nc 16 rng, bn chng ct v dn thu lc (Nagaraj et al., 1994).

1.4. THNH PHN KHONG VT

c trng ca pha rn da trn kch c ht v cc gii hn .st c th khng thch hp gii Ihch hnh vi k thut m cc t t nhin biu hin. c bit i vi phn ht si, c cc hnh vi khc nhau rt ln. Thnh phn khong vt ca t cho mt s u mi v cc c trng ca t st. gii thiu thnh phn khong vt, ta cn nh l s hnh thnh t da trn s phong ho dn n tri qua cc khong thi gian v cng ln. Ct v bi pht trin u tin t v ri b phong ho thnh ht st. Do vy hp l cho l ct v bi c thnh phn khong vt gn vt liu gc hn l st. Ct v bi c cha mt s khong vt nguyn snh hay khong vt gc - t nhiu khng b bin i t gc. St cha cc khong vt th sinh to thnh do phong ho cc khong vt nguyn sinh c sc khng km. T l tng di cc khong vt th sinh trong ct, bi v st c thy dng s hnh 1.14.

Hnh 1.14:T l tng di cc khong v nguyn sinh v th sinh trong t

25

Mt s khong vt nguyn sinh v th sinh c lit k trong bng 1.1. Mt tnh cht quan ng c trng cho tt c khong vt l lin kt gia Si v o . Thng thit lp t s molar ca hai nguyn t ny nh l ch bo v sc khng ca khong vt. Cc khong vt c t s molar cao l 0,5 (thch anh v fenspat) th rt n nh v chng li phong ho mnh hn cc khong vt c t s molar thp nh olivin - c t s molar l 0,25. Cc ht thch anh to trc tip t gc v bn vng ngay c trong cc khong vt th sinh, cng vi cc sn phm phong ho ca cc khong vt nguyn sinh c sc khng km hn.

Bng 1.1. V d cc khong vt nguyn snh v th sinh

Khong vt nguyn sinh Khong vt th sinh

Thch anh (Si02)

Fenspal (Na, K)A102[Si02]3

Mica K2A120 5[S20 5]A14(0H)4

Pioxcn (Ca, Mg, Fe, Ti, Al)(Si, Al)0j

01ivin(Mg, Fe)2Si04

Kaolinit [Si4]Al4O10(OH)8

I1(K, H20 )2(Si)g(Al, Mg, Fe)4 6O20(OH)4

Clorit (OH)4(SiAl)8(Mg, Fe)6O20

Monmorilonit Si8Al4O20{OH)4nH2O

Thch cao CaS04.2H30

Hu ht t st cha hn hp cc khong vt l tng c thnh phn bin i. Mi loi khong vt tc ng ti t, chia s cc tnh cht k thut cho t; v th hiu bit v hnh vi ca cc khong vt l tng rt c ch hiu hnh vi hp th ca t st. Do vy, chng ta nghin cu thnh phn cc khong vt tng ring bit v xut mt s c trng chung cc khong vt l tng tc ng n hnh vi hp th ca t st.

Cc khong vt hnh thnh trong t nhin tng ng vi trng thi nng lng nh nht c th c. l nh lut kinh t c tun theo ph hp s sng to. Nhm hnh thnh vi kh nng nng lng nh nht, ba iu kin phi tho mn l:

1. S thnh to din ra kt hp tt c cc nguyn t c th dng c r rng, cc nguyn t dng nhiu nht trong t nhin s xut hin thng xuyn trong cu trc khong vt.

2. Cc nguyn t hnh thnh khong vt phi theo mt s dng hnh hc m c th t lp li trong khng gian.

3. S thnh to lun c hng in tch trung ho, iu ny c to ra bng cch thay th cc anion v cation:

xem xt iu kin dp ng nh th no, chng ta lu s phong ph tng i ca cc nguyn t khc nhau trong v qu t. Nh thy bng 1.2, oxy, silic v nhm l ba nguyn t phong ph nht, chim 46,6%, 27,7% v 8,1% v trng lng v 93,8%,0,9% v 0,5% v th tch. Do vy trong t nhin, ba nguyn t ny c mt ph bin trong tt c cc khong vt (xem bng 1.1). iu kin 1 c p ng qua s dn xp cho ph hp tt c cc nguyn t ny trong thnh phn khong vt. iu kin 2 tham gia

26

vo s sp xp ng gi ca cc nguyn t. Cc nguyn t t ng gi vi nhau theo cch Ihc khng gian hiu qu nht. V th, hy vng l cu trc ca khong vt theo dng cc nguyn t nh chim ch cc l hng to bi cc nguyn t ln hn. Tuy nhin, s sp xp ng gi phi ng thi tun th iu kin th ba l din tch trung ho. Nh thy bng 1.2, oxy l anion ch yu nht trong v qu t v ch l anion c mt qu t n hn 1% trng lng. Do vy, iu kin trung ho in tch sai khin oxy c mt d dt Irong sp xp ng gi vi cc cation. Ngoi oxy, F v c r l cc anion cng c quan st trong sp xp ng gi ca cc nguyn t mc d chng l nguyn t him. Tri ngc vi cc anion, kh nhiu cation c bn knh ion khc nhau c th dng c. iu ny lm cho n c kh nng cn bng in tch m ca o theo mt s cch thc khc nhau. Cc cation tranh ginh tham gia vo cu trc khong vt. Cation tr tnh tham gia cu trc s ph thuc vo bn knh ring ca cc ion v kh nng thc hin trung ho in tch. Bng 1.2 cho bit ho Iri v bn knh ion ca cc nguyn t ch yu trong v qu t.

Bng 1.2. Phn trm trng lng v th tch trong v qu t, ho tr, bn knh ion v h s bn knh (i vi oxy) ca cc nguyn t phong ph nht trong v qu t

Nguyn t Trng lng(%)

Th tch(%)

Ho tr Bn knh ion ()

H s bn knh

0 46,6 93,8 -2 1,32 -

Si 27,7 0,9 + 4 0,31 ~ 0,39 0,23 - 0,30

AI 8,1 0,5 + 3 0,45 - 0,79 0,34 - 0,60

Fe 5,0 0,4 + 2 0,67 - 0,82 0,51 - 0.62

Mg 2,1 0,3 + 2 0,78 - 0,89 0.59 - 0,68

Na 2,8 1,3 + 1 0,98 0,74

Ca 3,6 1,0 + 2 1,06-0.17 0,80 - 0,89

K 2,6 1,8 + 1 1,33 1,0

S chn dn khong rng hiu qu ca cc nguyn t khc nhau ph thuc vo h s bn knh - t s bn knh cation vi bn knh anion.

S to l s cc anion b tr quanh mt cation, ti l thun vi h s' bn knh. H s bn knh cho trong bng 1.2 i vi oxy c thc hin cho hai loi sp xp. Mt l sp xp dng bn mt vi s to l 4 v h s' bn knh l 0,22. Loi sp xp khc c dng tm mt vi s to l 6 v i hi h s bn knh l 0,41. Cc h s bn knh ny l cc gi tr gii hn, ni cch khc, chng l h s bn knh thp nht i hi t c cch sp xp bn mt hay tm mt. Do vy, chng ta ghi nh l c kh nng

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cao Si tham gia vo sp xp bn mt, v Ai, Fe v cc nguyn t khc tham gia vo sp xp tm mt vi o . C hai cch sp xp nv l cch sp xp ph bin nht trong khong vt v c thy dng s trong hnh 115. Cn nh l s ph bin (thy trong hnh l./5b) ch cho mt cch nhn d hiu v cu trc; trong thc t, cc nguyn t kh gn nhau (hnh 1.15a) vi cc anion che khut cation.

Hnh 1,15: sp xp dng gi lng khi bn mt v tm mta)To thc v b) L tng.

Mt khi bn mt n c in tch m thc l -4 v mt khi tm mt c in tch m thc l -10. iu kin trung ho in tch buc cc n v c bn ny t lin kt vi cc n v tng t khc. V th, cc lp bao gm cc n v phi trin ny. V d, mt lp bn mt hnh thnh khi in tch m thc c xu hng trung ho ho bng cch chia x oxy vi bn mt bao quanh. Tng t, mt lp lm mt hnh thnh do s chia x cc anion bi khi tm mt k cn. Cc lp ny c thy trong hnh 1.16 cng vi cc k hiu dng hin th chng nh l cc khi cng trnh trong cc khong vt. Chng l cc lp c s nht tn ti trong cc khong vt st.

b)

Hnh i.l : Cc lp hn mt ) \ (m mt (b) cng vi cc ch dn v k hiu

iu kin trung ho in tch i hi cc lp ny lin kt vi mi lp khc theo phcmg ng cng nh vi cc lin kt ho hc gia cc lp. Lin kt ion lin quan vi s chia x cc on, l lin kt mnh nht v d dng c c gia lp bn mt v tm mt. S chia x cc anon ti mt phn cch hai lp lm cho in lch trung ho. S ng gi cc lp nh th to ra cc n v di c bn hay bn c bn. Thut ng dng cho dn v to thnh gia mt lp bn mt v mt lp tm mt l 1 : 1. n v quan trng

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khc hnh hnh khi mt lp tm mt b kp gia hai lp bn mt vi cc lin kt ion trn mt kia cua lp tm mt v c biu th l 2: i. Hai n v di c bn thy trong hnh 1.17, cng vi thnh phn cc khong vt chnh gp trong t st.

Hnh . 17: Cc n v di c bn : 1 (a) v 2 : (b) cng vi cc ch dn k hiu ca chng

Tht quan trng nhn mnh l do s bin i cc cation c th c trong v qu t, s cc cation khc nhau c th c mt trong mt n v bn c s cho. Bn knh ion ca mt s cation (bng 1.2) thch hp v kch c d to nn s b tr bn mt hay tm ml vi cc anion. V d, lp bn mt c the cha cc ion A l3+ hay Fe',+ v lp tm mt c the cha cc ion Al3+, Fe2+, Zn hay Ni. D nhin, cc thay th nh vy din ra c lu n iu kin trung ho in tch. Khi mt ion ho (ri ba nh A l3+ c mt lp tm mt, khng quan st thy cation trong mi tm mt th ba l do iu kin trung ho in tch ny. S (hay th rt ph bin trong nhiu khong vt, gi l thay th ng hnh. Phn ln kh nng thay th ng hnh lm cho t st c phm vi rng v hnh vi k thut. Ngoi ra mt s kh nng ny sinh do s sp xp ca hai n v di cbnring l hay c kt hp, do vy biu hin cc tnh cht k thut khc nhau nhiu.

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Trc khi chng ta trnh by khi qut cc khong vt ph bin, iu quan trng cn ghi nh l iu kin trung ho in tch c th p ng mt phn bi mi trng lng bao quanh cc n v di c bn. S trao i cation c th xy ra gia cation trong dung dch v cation trn b mt n v, do vy cn bng in tch thay i. in tch dng tng m mt khong vl cho hp th th bng din tch m thc ca n. Kh nng hp ph cc cation ny ca khong vt gi l kh nng trao i cation (CEC: cation - exchange capacity) ca t. N biu th bng mili ng lng ca cc cation c hp ph cho mi lOOg t kh (mEq/lOOg), tng ng centimole ca in tch dng cho mi kg t kh. CEC l mt dc tnh quan trng ca khong vt, n khng ch cc tng tc gia pha rn v cht lng trong l rng.

Cc khong vt ph bin hnh thnh do s sp xp cc n v di c bn c thy trong hnh 1.18. Mt s tnh cht quan trng ca cc khong vt ny lit k trong bng 1.3 v cc dc trng ca chng c trnh by khi qut cc nt ch yu di y.

y> = =

Haloysit c cu trc lp 1 : 1 tng t nh kaolinit, tuy nhin gia cc lp c mt di phn t nc, do vy n v sp xp c b dy ln hn. Khi kh nc, haloysit xp li khng thun nghch sang cu trc kaolinit.

Hit hnh thnh do cc n v sp xp dng 2 : 1 gn kt vi nhau bi cc ion kali. in tch m hp dn cc ion kali l do s thay th' nhm cho mt s silic trong cc lp bn mt. Cu trc ilit tng t cu trc khong vt mica nguyn sinh, ch tr kt tinh km hn v cha kali t hn. Cc ion kali bn vng gia cc lp, ngn chn s trng n ca khong vi v cho din tch b mt trao i cation gia cc lp khng ng k.

Vecmiculit c cu trc lp 2 : 1 tng t ilit, nhng cc n v di c s trong trng hp ny b chia tch bi mt cp cc lp phn t nc. Trong khong vt ny cng pht hin mt s silic c nhm thay th lm cho in tch m thc th cao.

Monmorilonit cng c cu trc lp 2 : 1 nhng c s thay th ng hnh rng ri ca magi v st cho nhm trong cc lp tm mt. Khng ging ilit, khng tim thy ion kali gia cc lp v khng ging vecmiculit, cc lp c chia tch bi mt s di phn t

, nc. Mt c trng khc bit ca khong vt ny l trung n mnh kh t trong nc do cc phn t nc xm nhp vo khong gia cc lp. Do gii hn chy ca monmorilonit rt cao.

Clorit thng dng gi lp silicat 2 : 1 : 1 do s c mt ca lp hidroxit kim loi kp gia n v 2 : 1. Di gia lp thng hiu l lp bruxit, tn ca khong vt bruxit c magi l cation trong s sp xp khi tm mt. Mt s thay th ng hnh ca Mg2+ bng Al3+ tn li trong lp trung gian ny. Do c mt lp ny, Clorit c din tch b mt v CEC thp khng b trng n trong nc.

Phi nhn mnh rng thnh phn ca khong vt l tng em c bt k c m t trn him khi biu hin ton b trong phn ht st. Mt s khong vt c mt trong t cho v mt hay nhiu khong vt ny c th ch ng thnh phn, nhng him khi t biu hin c trng qu mc ca mt khong vt l tng. Cc lp tip theo c th thuc

. v cc khong vt khc nhau. Chng c th khng uc lin kt vi nhau theo cch uc khi qut ho. Cc khong vt c lp hn hp ny c th c cu trc d don (chng hn mi lp khc l ilit hay monmorilonit) hoc cu trc hon ton ngu nhin.

] .5. VAI TR CA THNH PHAN n h n h VI K THUT CA T

Trong mc ny chng ta xem xt nh hng ca thnh phn n cc tnh cht k thut ca t. c trng c bn hay du hiu ca t thng c quy nh bi thnh phn khong vt. Vi phn trm pha rn cho trong t, c th d bo c st ca t qua thnh phn khong vt. Bng 1.4 cho thy phm vi gii hn Atterberg cho cc khong vt trnh by mc trc.

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Bng 1.4. Gii hn Atterberg v hot tnh cua cc khong vt st l tng

Khong vt Gii hn chv(%)

Gii hn do(%)

Gii hn co ngt(%) Hot tnh

Kaolinit 30 - 100 25 - 40 25 - 29 0,5

Haloysit 50-70 47-60 0,1

Ilit 60 - 120 35-60 15 - 17 0,5 - 1

Monmorilonit 100 - 900 50-100 8,5 - 15 1 -7

Clorit 44-47 36-40

* Hot tnh ca t l t s' ca ch s do (gii hn chy - gii hn do) vi phn trm phn ht c kch thc < 2fim (theo Mitchell 1993).

D nhicn mt trong nhng nh hng tc dng quan trng nht ca thnh phn khong vt c licn qan vi s tng tc gia cc pha rn v ch lng l rng. S khc nhau ln v din lch b ml khong vt to ra s khc nhau trong vn chuyn khi ca cc cht nhim gia cht lng l rng v lc ht dnh ca pha rn. S khc nhau v CEC cng lm cho tnh dn ca t khc nhau. in tch m khng cn bng ca khong vt (c phn nh bi CEC) khin cc khong vt tng tc vi cc cation c mt trong cht lng l rng. S trao i ion ny gia pha rn v pha lng lm bin i s cn bng in lch ca cc ht. Trong chng 2, chng ta s nghin cu in ho ti b mt st ng vai tr quan trng trong vic nh hng cc ht nh th no v cc l rng dc hnh thnh ra sao. Kt qu cui cng ca tng tc ny t bin i hin tng dn truyn ca t. Dn chng ny th hin khi chng ta tho lun l thuyt lp kp trong chng 2, cu trc m khi t dt c ph thuc vo cc tng tc gia cc pha rn v cht lng l rng.

T l tng i ca pha kh v pha ne trong t bin i cng ng vai tr quan trng trong kh nng vn chuyn ca t, nc v kh c th vn chuyn d dng trong t hay khng c lin quan trc tip ti t l th tch ca cc pha ny. S cng tn ti ca hai pha ny trong khong trng l rng to ra mt s yu cu khc thng khi m hnh ho hin tung lan truyn khi v vn chuyn cht nhim. Ni dung ny c cp n trong chng 3 v 4.

Mc d c nh hng n mt s tnh cht k thut quan trng, nhng thng b qua s c mt vt cht hu c c trong t. Vt cht hu c, c khi c t l th tch tng i nh, c tc ng ln n kh nng hp ph nc. S quan trng ca vt cht hu c c m t r nht trong hnh 1.19; hnh cho thy gii hn chy tng khi lng cacbon v monmorilonit tng ln. R rng l ch n thun 5% cacbon hu c s lm tng gii hn chy ca t nhiu hn l khi tng l l momonrilonit ti 80%. nh hng cng nh

32

Chng 2

CU TRC T

2.1. G I I T H I U

Nh ta Ihv trong thng , trong cc giai on thnh to thin nhin to ra kh nhiu thnh phn t khc nhau. Khi cc bin i thm do con ngi gy ra nh qu trnh xy dng (chng hn nh m cht), th nhim v xc nh s bicu hin vt l ca t tr nn rt kh khn. Thut ng kt cu thng dng chi' s sp xp vt l cua cc ht ring bit trong t, Chng t'd s xem xt vn tt s nhn bit mt "ht", bn thn n l mt vt cht nh gi trong t st. Nhm cc ht nh st n c khi hp th li thnh cc loai t khc nhau gi l mt ht. Thul ng cu nc c dng khng ch cp s sp xp vt l bn trong t nh kt cu, m cn cp n s n nh hav s ton vn ca . Yong v Sheeran (1973) nh ngha kt cu l "s sp xp vt l ca cc hl t v bao gm khong cch ht v s phn b' kch c l rng", cn nh ngha cu trc ca t l "tnh cht ca t cho kh nng ton vn ca n". Ngoi khong cch cc ht v s phn b kch c l rng, cu trc ca t cn bao hm thnh phn khong vt v ho hc ca ba pha c nh hng n cc lc gia cc ht. Mc d hai thut ng kt cu v cu trc thng c dng dng ngha, s khc nhau ln l trong cc nh vc m s n nh vt l ca t [ quan trng. V d, bn cht nhy cm ca t chy, st l v trng n khng gii thch c nu ch xem xt ring VC kt cu; m cn phi xem x! nh hng ln nhau ca cc lc l ho gia cc ht hay cc nhm ht.

Hu ht cc nhn thc hin thi v cc ht t nhm li vi nhau nh th no l da ircn cc quan st bng knh hin vi quang hc hay in t, V d, hnh 2.1 cho thy vi nh ca su vt liu khc nhau c cng phng i. Do nh gi ch quan lin quan vi s quan st m hnh, thut ng lcn quan vi cu trc t rt rng. Nhiu thut ng thng dng ln xn mc d cc nh ngha ca chng l cht ch trong cc mn hc khc. Mt v d th v l cch s dng cu trc kt bng v hp th. Cc thut ng ny dc dng ng ngha, mc d thut ng sau c dng ch khng phi s kt bng thun luv gia cc ht m l s kl hng c gn kt.

S quan lm ca chng ta trong nghin cu cu trc l xut pht t thc t l cu trc ng vai quan trng rong cch thc cc cht nhim c vn chuyn trong l. rng v s phn b kch c l rng ph thuc trc tip vo c trc t. Cc thng s ny khng ch cc c trng lan truyn v vn chuyn khi trong t. Chng ta s bt u vi s tho lun v cu trc i c nhn thc tai cc quv m quan st khc

34

nhau nh th no v ch trng vo s sp xp ht nguyn t tham gia vo cc c trng khc thng ca t cho. Trong qu trnh ny, nghin cu khong vt st v cc lc gia cc ht hot ng ti quv m ca mt bn st ring bit.

Ilnh 2.1: Cc v d v cc vt liu rng t nhin (XJO) a) Ct bi bin; b) Ct kt; c) vi; d) Bnli m mch en; e) G;

f) Phi Iigi. (Theo Collins, 1961).

2.2. CC QUY M CU TRC T KHC NHAU

Theo quy m quan st khc nhau, cu trc t biu hin cc cch khng ging nhau. Quan st bng mt kch thc v hnh dng cc cc t ring bit, ta c th biu th c im tng i d dng mu t lp trn cng - th nhng. Khi kho st cct bng knh hin vi c th thy cc ht ring bit c sp xp khc nhau v ccnhm ht, biu th c im l cn phi c thm mt s thut ng.

Cc cc t c th thy ta nh cc hp th. Cc hp th ny c phm vi kch thc t hng milimet n vi centimet. B Nng nghip M (USDA) a ra s phn loi cu trc ca hp th da trn kch thc v hnh dng ca chng. S phn loi ny, c thy trong bng 2.1, dng ch yu ba khi nim m t c trng kch thc v hnh dng: dng tm, dng lng tr v dng khi. Ba yu t c bn ny c thy trong hnh 2.2. Cu trc dng tm khi c trc nm ngang di hn trc thng ng (E trong hnh 2.2), trong khi cu trc lng tr th trc thng ng chim u th. Cu trc dng ct khng c chp trn c gi l lng tr (A) v c chp trn gi l ct (B). Cu trc khi c dng biu th cc khi hp th c kch thc ti 10cm, vi cc mt phng c gc (C) hay hi c gc (D). N cng hao gm cc hnh phng cu nh hn c chia nh them thnh cc t, hay cc ht nh (F) da trn chng biu hin c l rng hay khng.

35

u>ON Bng 2.1. Cc loi v s phn loi cu trc t

Lp

Loi (dng v s sp xp)

Ging hnh tm vi mt kch thc (thng ng)

gii hn v km hn nhiu hai kch thc

khc; sp xp quanh mt mt phng nm ngang; cc mt hu ht nm

ngang

Ging hnh tr vi hai kch thc (nm ngang) gii hn v tng di nh hn kch thc

thng ng; sp xp quanh mt dng thng ng; cc mt

thng ng xc nh r

Ging nh khi, khi a din hay hnh cu, vi ba kch thc c cng ln c b tr xuag quanh mt im

Ging nh khi; cc khi hay da din c cc mt phang hay cong

Dng phng cu hay a din c cc mi phng hay cong; cc

mt ny t hay khng thun tin cho cc mt xung quanh

Khng c chp trn

C chp hnh trn

Cc mt dc dt phng hu ht cc chp l gc nhn

Cc mt trn v dt phng hn hp vi

nhiu chp trnTng i khng rng Rng

Tm Lng tr Ct Khi gc cnh Khi bn gc cnhb Dng ht Mnh vun

Rt mn hay rt mng

Tm rt mng; < mm

Lng tr rt mn; < lOmm

Ct rt mn; < lOmm

Khi gc cnh rt mn; < 5mm

Khi bn gc cnh rt mn;< 5mm

Ht ri mn; < Imm

Mnh vn rt mn; < lmm

Mn hay mne

Tm mng; 1 - 2mm

Lng tr mn; 10 - 20mm

Ct mn; 10 - 20mm

Khi gc cnh mn; 5 - IOmm

Khi bn gc cnh mn;

5 - Omm

Ht mn; 1 - 2mm

Mnh vn mn; 1 - 2mm

Trungbnh

Tm trung bnh; 2 - 5mm

Lng tr trung bnh;

20 - 50mmCt trung; 20 - 50mm

Khi gc cnh trung bnh; 10 - 20mm

Khi bn gc cnh

trung bnh; 10 - 20mm

H trung; 2 - 5mm

Mnh vn trung;

2 - 5mm

Th hay dy

Tm dy; 5 - 10mm

Lng tr th; 50 - 100mm

Ct th; 50 - lOOmm

Khi gc cnh th: 20 - 50mm

Khi bn gc cnh th:

20 - 50mmHi th;

5 - lOmm

Rt th hay rt

dv

Tm rt dy; > lQmm

Lng tru rt th; > 100mm

Ct rt th; > OOrrn

Khi gc cnh rt th; > 50mm

Khi bn gc cnh rt th;

> 50mm

Ht rt th; > Omm

a- Di kii gi l ht, h t "c cnh" thng c qun (li. h- i khi gi l (lit qu hch.

Mc d s phn loi cu trc dt ca USDA cho phng thc n gin biu th c im cc hp the, n khng cho php chng la tip cn cc quy m nh hn phm vi kch thc trng thy. Chnh ti cc quy m nh, cu trc t s ng vai tr quan trng, d lm bin di s phn b kch c l rng v cc tng tc ho hc xy ra gia cht lng l rng v pha rn. Kh khn khc lin quan vi s phn loi ca USDA l thc t khng c kh nng gn mt kch c tuyt i cho hp th trng thy bt k ngoi tri l do hp th lun c th v ra thnh cc nhm ht nh hn.

Hnh 2.2: Cc loi cu irc dt A - lng tr; B - ct; c - khi gc cnh;

D - khi hi gc ct lit; E - tm;F - ht {theo SDA, 195n .

S phn b cc nhm ht do vy ph thuc vo phng thc c hc dng chia tch chng t hp th khc.

iu dn chng la cn xem xt cc c trng ca cu irc t quy m nh hn. Collin v McGrown (1974) nghin cu cc cu trc biu hin ca t st, hi v ct dc c kt thng thng hay hi qu c kt t cc v tr a l khc nhau. Cc loi t ny lin quan vi cc mi trng v cc qu irnh trm tch khc nhau. Hai loi sp xp khc nhau trong nghin cu ny l:

Loi 1: ht nguyn t sp xp bao gm cc ht st, bi v ct dn Ic.

Loi 2: cc tp hp ht bao gm mt hay nhiu dng sp xp ht nguyn t hay cc tp hp ht nh hn.

Hnh 2.3: Biu hin s cc sp xp ht nguyn t a Tng tc tm st nho dn l; b) Tng tc ht bi hay ct dn l;

c) Tng tc nhm di st; d Ttig c ht bi hay ct dc bao ph; e) Tng tc ht ch c th dc mt phn (theo Collin v McGrow ft, 979).

37

Hai loi sp xcp ny licn quan vi cc quv m khc nhau ca l rng s tho lun sau. Hnh 2.3 cho thy s sp xp [oi 1 li quy m ht. Rt c kh nng l t cho biu hin nhiu hn mt ca cc sp xp cnh nhau. Mt quan st quan Irng cng c s c trng ny l t ca cc mi trng khc nhau v cua cc kiu trm tch khc nhau biu hin cc sp xp tng t nhau. Hnh 2.4 cho thy s loi sp xp2, chng l cc tp hp v do vy c quy m kch thc cao hn phn no. Mt s nh chp hin vi do Collins v McGrovvn (1974) cng b dng nh gi ln l c kh nng VC phc cc ng bin cua tp hp. Ngoi ra. cc tp hp tng t tm thy c m trong t c cc yu l mi trng v trm tch bin i rng, nhng vn c the s dng s c trng (ng qut.

linh 2.4: Biu hin s cc p hp hi a , b, c) Cc vt ni !in; ii Cc lp lkh/tg qav tc dc lin kt

bng cc tp tp ni in; e) Cc hp ikhng c/iiy tc hnh thnh s sp xp hnh trang In' t oii; f) Cc ihm h! qv tc tng tc vi cc hi bi hax ci;

g) Hp th c quy rc tiH lc vi khi ht; h) Cc chm st c dan vo nhau; j) Cc chm st dc (lu vo nhau vi cc th vi l bi; k) Khi hat st; I) Khi h! dng ht.

2.3. KCH C L RNG LIN UAN VI CU TRC T

S ph thuc quy m ca cu trc t phn nh trong s bin i mnh kch c lrng ca t. Biu th c icm cc l rng c lin quan vi cu trc t cho l mt

, Hon hap'X t:

I)

38

nhim v kh khn. Dullien (1992) ghi nhn kh khn ny khi ni "Khng c th nh ngha hon ton tng qui v l rng, mt l rng c nh ngha l mt phn ca khong trng c bao bi cc b mt pha rn v bi cc mt phng dng ln ni bn knh thu lc ca khong trng biu hin li thiu, tng t nh mt bung c nh ngha gm cc tng v cc ca s c m ra cho n". Hnh dng v kch thc cc l rng l cc k quan trng gip chng ta nh lng lu lng v nh gi s nh by cc cht nhim. Cc ni dung chi tit v ba kha cnh ny s c trinh by trong ba chng lip sau, y chng ta ch yu xem xl vn d ph thuc quy m ca c icm l rng.

S tn tai cc hp the i VI cc 16 rng r cy, khe nt v vt nt cho quy m ln nht ti d c the m t c im l rng. Cc l rng ny to nhm cc l rng quan trng cn b trnh nc l do khng th m phng chng Irong phng th nghim v do vy khng th d on thch hp nh hng ca chng n s vn chuyn cht nhim ngoi tri. Phm vi kch thc tip iheo ca i rng hnh [hnh do s sp xp ca cc tp hp ht. S quan trng km hn l v kch thc ca chng nh hn v cc l

Hnh 2.5: Phn loi l rii theo Osen 1962)1. Cc l rt trong chm;2. Cc l l ii gia cc chin.

rng hnh thnh bn trong s sp xp ht nguyn l. Olsen (1962), nh ngha hai loi l rng, l rng gia cm v l rng bn trong cm, y cm c xem l mt nhm cc ht hay t hp ht Ihnh n v ln hon (hnh 2.5). S phn loi ny c Olsen dng quan st s ng gp lng i ca hai nhm l rng v nghin cu nhhng cua hp th ht n tc thm qua t.

Collins v McGrown (1974) a ra s phn loi khc da trn cc quan st v kt cut cp trcn. Bn loi l rng c c ngh trong nghin cu ny l:

1. Cc l rng bcn trong nguyn t tn li bn trong cc sp xp ht nguyn t khc nhau, bao gm c cc l rng bn trong ht v cc l rng bn trong nhm (cc l rng ny tn ti gia cc nhm ca cc phin st).

2. Cc l rng bn trong t hp tn ti trong cc t hp ht hay gia cc t hp ht nh hn trong mt t hp in hn.

3. Cc l rng bn trong t hp ln ti gia cc t hp ht.

4. Cc l rng xuyn qua t hp, chng ln hn v kch thc so vi cc l l n g khc, vt ngang mt s t hp trong kt cu t.

39

Bn loi ny c thy theo s hnh 2.6. Thng kh khn phn bit cc l rng trong v ngoi t hp, v tng t gia l rng bn trong v xuyn qua t hp. V l do nv, s chia nhm c th khng thc t, ch c ba nhm l thun tin do Matchell (1993) da ra ba kt cu ny l kt cu vi m, nh v v m. Kt cu vi m bao gm cc sp xp ht nguyn t vi cc l rng rt nh gia chng, kt cu nh bao gm cc l rng gia cc t hp v kt cu v m cp n cc l rng xuyn qua t hp gm c cc khe nt, ng nt, cc hc r, thng hiu rng dng cht lng qua t b khng ch trc tin bi cc kt cu nh v kt cu v m ca t, cn kt cu vi m t nh hng dcn.

Hnh 2.6: Biu hin s cc dng khoi rng (ileo Collins v McCirown, 1974)

2 .4. S SP XP CC HT N

Sau khi xem xt s phc tp v c trng ca cu trc t v l rng c lin quan, nav la tin hnh nhn bit c cu lin quan trong khi nhm cc ht quy m nh nht. Chng ta s xem xt vn tt s ln cc lc l ho hot ng ti quy m ca mt ht n l cho hp th trng thy c ca t c cu trc phc tp. S hu ch cho la khi bt u bng ct v bi, l v cc sp xp dn gin hn st rt nhiu. Khng ging st, trong sp xp ht ca ct v bi ch c t tng tc ho hc.

S cch thc m cc ht hnh cu c cng kch thc c ng gi gii hn. Do ng nht, ta c th chn cc ht ny. v c kh nng d on v ton hc th tch khong rng chim ch cho cch sp xp chn d cho. Hnh 2.7 cho thy nm kiu sp xp chn lp c quy lut ca cc hnh cu bng nhau! S sp xp khi thy trong trng hp a) p ng dung trng nh nht v rng ln nht vi s' to (cc im tip xc cho mi hnh cu) l 6 v rng th tch trung bnh l 47,64%. sp xp lng tr v t

40

din cho Irng thi ng gi cht nhl vi s to l 12 v l rni th lch trung binh l 25,95%. Bang 2.2 cho thy cc tnh cht ca cc ng i bnh thng trung gian.

Bng 2.2. Cc tnh cht ca cc sp xp ng gi theo quy tc cc khi cu c cng kch thc (theo Deresicwics, 1958)

Loi ng gi S lo Khong cch lp (R - bn knh)

Th tch ca n v

rng(%)

H s rng

Khi n 6 2R 8R3 47,64 0,91

T din - khi 8 2R W 3R3 39,54 0,65

Cu - f din 10 r V3 R3 30,19 0,43

Lng tr 12 r V2 W 2 R3 25,95 0,34

T diu 12 2RV2/3 4 V2 R3 25,95 0,34

Hnh 2.7: M lli ng gi theo qu\' c ca cc litli cu c cng kch thca) Kii dn; h) Tcin khi; c) Hnh cu - t din; d) M/Ig tr; e) T din.

(ngun: Deresiewics, 1958)

Tng l cc ng gi thng thng, ng gi ngu nhin cng phi hin thy c lin quan vi phm vi c trng cua rng. V d, Haughey v Beveridvc (1969) chia ra bn kiu sp xp ng gi ngu nhicn vi phm vi rng hp cho mi cch sp xp: 1) ng gi ngu nhin rt lng lo vi rng khong 0,44, nhn c bng cch gim chm tc trong lp ho lng; 2) ng gi ngu nhin bng tay lng lo vi phm vi rng 0,40 - 0,41, nhn c bng cch ng gi ngu nhin cc ht n l; 3) ng gi ngu nhin bng cch rt vi phm vi rng l 0,375 - 0,391, khi cc hnh cu c rt vo trong cc ng; 4) ng gi ngu nhin cht vi d rng 0,359 -0.375 nhn c khi ng gi bng cch rung hay lc mnh. Ni chung, s to l i din ca kt cu v c th dng suy ra rng. Ridway v Tarbuck (1967) cho quan h hi quy gia s to u v rng n nh sau:

41

n = 1,072 - 0 ,1 93u + 0,004312u2 (2- 1)

Cc quan h tng t gia rng v s to c trong cc sch. Cn cn thn khi p dng cc phng trnh hi quy ny cho cc h a phn tn - h c kch c hnh cu bin di, do cc quan h rt phc tp. Ni chung, rng ca cc h t nhin hao gm ct v bi c kch thc bin i nm (rong cc gii hn l thuyt ca cc sp xp ng gi cp trn.

Trong trng hp st, s sp xp cc ht n l bin i ln do thnh phn khong vt cc ht thay i v lin kt kh phc tp vi nc l rng. Cc nghicn cu bail uch tp trung vo s sp xp ht trong th vn. Mc d c cc yu t' ph thm xemxt cc khi d thc, hiu bit v s sp xp hc trong cc ih vn st l bc quan trng u tin hiu cu trc ca st. Hnh 2.8 cho thy cc kt hp c th c gia cc ht scl trong th vn. Thut ng lin quan vi cc kt hp ny nh sau:

Phn tn: khng kct hp mt vi mt gia cc ht tn ti.

Hp the: kt hp mt vi mt cua mt s ht tn ti.

Kt bng: kt hp gc vi mt hay gc vi gc ca cc ht ln li.

Tan kt bng: khng kt hp gc vi mt hay gc vi gc gia cc ht tn ti.

Hnh 2.8: Cc kiu lin kt hi trong cc th vn sl v thut n a) p/tt ln v ln k bng; b\ Hp llilihng lun kt bnt;

c) K! bng C vi mt nhng phim ln; d) K) bng gc vi gc nhng phn ln; e) Kt bng gc vi mt nhng hp th; f) Kt bng t>c vi gc nhng hp th;

g) Kt bng gc vi mt \' gc vi gc v hp th (theo Van Olphen, 1977.

Hiu bit cc yu t chu trch nhim cho cc kt hp khc nhau thy trong hnh 2.8 l c s d t nht d on c nh tnh cc bin i c trc ca st do cc yu t mi trng. iu ny dn n vic nghin cu cc tng tc st - nc do s phn b cc ht st ring l din ra qua mi trng ca mng nc b ht v cc ht st. Hai c cu u tin set v nc hp dn nhau l: i) Bn cht ng cc ca phn t nc ko cc phn t nc v gn cc ht st tch in m v 2) Cc cation bt k tn ti gn ht st

42

c xu hng b ht v ht st mang theo chng nuc ca thu ho. Mitchell (1993) chia nh cc c cu ny thnh bn c cu ricng (hnh 2.9):

1. Lin kt hydro gia hydro v cc phn t nc v oxy hay hidroxin ca cc b ml ht sl.

2. Thu ho cc cation ln cn cc ht set.

3. Hp dn thm thu do nng d cc cation gn b mt ht tng v chuyn ng ca phn t nc thun hng v pha h mt ht cn bng nng .

4. Hp dn trc ticp gia lng cc nc v b mt ht tch in do lc thu ho mnh ca b mt v dch chuyn thun hng ca cc cation xa khi b mt.

h 1^ 3 1a |rl I j i;30-

i 0.........I ^ Gx . Nn d lon lnq ln

j o o o 1 ! " 0 1 1 3 0

] '

o oJ0

Nc lng cc

0 O w> 0 ^

(?) S khuych tn hng7 \ ^ ^''-voc phn tmc

) e f7

G G G e G e eO O O Q

e O Q C G 0 t

c)

Hnh 2.9: c 'c kiu hp dn gia nc v b mt ht st Liti kt hydro; b) lon r//v IO; c) Hp dcn bi im thu; d Hp dn ng cc

(theo Mitchell, 1993)

Cc lc ht nc v ht st gim theo khong cch - Lambe (1958) chia nc b ht ihnh ba loi da trn ln tng i ca lc ny: nc hp ph, nc lp kp v nc t do. Nc hp ph c b dy chi vi phn t (vo khong 10) c gi bi cc lc mnh m V I cn ti lO.OOOatm c th ko cc phn t nc ra khi b mt. Nc lp

43

kp trong mt s thut ng phn loi thng gp vi nc hp ph, c ht bi cc lc km mnh hn, d cho dng thm in ra song song vi b mt ht nhng kh ko nc m khng thay th lin c. R rng, b dy cc lp ny ph thuc vo mt in tch ca b mt ht, trong cc thng s khc. Mt in tch cng cao th b dy cc lp ny cng ln v ngc li. Hnh 2.l0a v 2.10b biu hin s ph thuc ca b dy cc lp nc ny vo mt in tch. Kaolinit c mt in tch cao nn lp nc dy hn monmorilonil. iu ny khng dn n kt lun l m ca h monmorilonit thp hn m ca kaolinit. iu tri ngc m thc l do din tch b mt c trng ca monmorilonit ln hn kaolinil nhiu. Vic xem xt lp kp l rt quan trng trong cc h t l v hu ht nc l rng trong l hin trng dc cha lp ny.

Cc ht ring bit tip xc nhau qua cc lp nc. S tng tc cc lc ca cc tp nc ca hai ht tip xc, kt hp vi cc lc bn ngoi v cc bin i mi trng khng ch s sp xp ht.

a) b)

Hnh 2.10: So snh b dy lp nc ) Tilth thmonmorihmt: b) Tinh thkaolinit (theo Lambe, 1958)

Hai b ml khong c lc no tin n tip xc vt l hay khng l vn cn tranh ci. Tuy nhin, cn c nhn thc v cc yu t khc nhau tc ng n cc lc hp dn v y nhau gia hai ht d hiu cc nh hng mi trng ca s sp xp ht. Vic x l thuyt lp kp da trn tnh in cho chng ta s hiu bit ny.

2.5. L THUYT GOUY - CHAPMAN v LP KP

Gouy (1910) v Chapman (1913) c lp tm c biu thc l thuyt cho th in trong lp kp, c kh nng cho chng ta xem xt nh hng ca cc tnh cht khc nha ca mi trng n b dy lp. L thuyt vin n v kt hp hai phng trnh (quen bit) ni ting, mt phng trnh biu th s bin i in th vi khong cch -

44

phng trnh Poisson v phng trnh Boltzmann biu hin quan h gia s phn b lon v in th.

Phng trnh Poisson biu hin l din th l/ gim theo khong cch t ngun, tc l < b mt ht st vi in th' m tng ln. S c mt cc in tch hay ion v hng s cht in mi ca mi trng khng ch s gim in th ny. Phng trnh thng biu th dng;

Trong : X - khons cch t ngun;

p - mt in tch;

e - hng s cht in mi ca mi trng.

Mt in tch trong mi trng l s gp phn cua cc anion v cation trong mi trng:

p = c(v+n+ - v_n_)

Trong : c - in tch;

V - ho tr;

n - s ion cho mi th tch n v;

+ v - di k hiu th hin cation v anion tng ng.

S in trong phng irnh (2-3) t khng ch in th ti.

Phng trnh Boltzmann cho ta quan h th hai i vi cc cation v anion:

(2-3)

(2-4)

(2-5)

Trong : n0 - mt ion xa b mt;

k - hng s Boltmann (1,38 X ic f23 JK_I);

T - nhit Kelvins.

Khong cch l ht

Hnh 2.11: S phn b cc ioti nm k b mt st mung diti tch m

45

Vi mt ht st, in th 1|/ l m, do vy lng cation tng v lng anion gim khi in th m tng. Khi coi rng in th V|J gim (hco khong cch t b mt ht st tch

in, s phn b cc ion c th biu th bng s nh thy hnh 2.11. Cho trng hp n gin cc ion cng ho tr, c th Ihay cc phng trnh (2-4) v (2-5) vo phng trnh (2-3) cho;

( 'p --2 n .,c s in h (2-6)U t J

Thay phng trnh (2-6) vo phng trnh (2-2) cho ta biu thc xc nh s bin di theo x:

d2u 8rtn,.c . , ( CV/ ^ 1 - sinh 3dx e vkT

Phng Irnh (2-7) c th n gin ho ihnh:

(2-7)

2

vi hai i lng khng th nguyn

d2y= sinhy (2-8)

y = ^ v C = kx (2-9)k.T

Trong : k = y 71- n (2-10)

By gi chng ta tm li gii ring cho phng trnh (2-8) vi hai iu kin bin c bit, mt ti b mt ht v mt khong cch ti ht l v tn. Cc iu kin bin y c th biu hin nh sau:

y = 0 v = 0 ti C = 00 (2-11)dC

v y = z ti C = 0 (2-12)kT

Ly in th ti b mt ht l y u. Vi cc iu kin bin ny, c th vit li gii phng trnh (2-8) nh sau (Verwey v Overbeek, 1948):

e > l ^ L t l g = i g (2-13,e + 1 - ( e y - l)e^

Phng trnh (2-13) bao hm s suv gim s m ca in th, gim t y = z(v/ - \f0) ti b mt ht n y = 0 (\> = 0) tai khong cch v cng t b mt hat. Theo Verwev v Overbeek (1948) c th thc hin mt s n gin ho cho [i gii ny i vi mt s trng hp c bit. Ba n gin ho ph bin l cho cc trng hp z 1, L - v cngv , 1. Vi cc trng hp ny, c th nhn c cc li gii sau:

46

- k xV - M\,e

2 k T ,_ KxV ------lncoth c 2

v V =4kT [ e ' /2 - l

" I ez/2 + 1

vi z 1

vi 7 = GO

vi z bt k v c 1

(2-14)

(2-15)

(2 - 16)

Phng trnh (2-14) thng c coi [ phng trnh Dcbye - Huckel v 1/K biu th chiu di c trung hay h dy lp kp (cng c gi l chiu di Debye). Vi cc in th bit, bng cc phng trnh (2-4) v (2- 5) c th nhn c cc phn b ion.

L thuyt Gouy - Chapmann c th m rng cho trng hp hai lp kp tng tc khi hai b mt st gn nhau. Trng hp ny thy trong s d hnh 2.12. Phng trnh (2-8) ln na khng ch s bin i in th mc d cc

Hnh 2.12: S d th hin s bin i in th gia hai mt song song khi so snh vi s bin i

in th'ca mt b mt n

iu kin bin khc nhau. Coi bin i th i xng gia hai mt, c th gii phng trnh (2-8) gia X = 0 v X = d vi cc iu kin bin sau y:

ctf dy y - _ v ti X = d

c kT d

v y = zkT

ti X = 0

(2-17)

(2-18)

Vi cc iu kin bin ny, li gii phng trnh (2-8) SC l tch phn eliptic di y v cn c gii bng phng php s:

1y

2(cosh y y - cosh yc)- Kd (2-19)

Verwey v Overbeek (1948) cho cc bng gii tm yc khi bit z v d. Vi cc trng hp c bit, ln na li n gin ho khi tng tc mnh (tc l yc 1) v khi tng tc yu. Trng hp sau c li gii rt n gin. in th ti mt phng gia c

47

th c c chng trong trng hp khi tng cc in tch ( y 'c ) do hai lp kp c lnh tch bit. V th:

yt.= 2 y ' (2-20)

Vi cc tng tc yu, nht thit rng. Do vy, c th dng phng trnh (2-16) lnh y^ , cho mt lp kp ring l khong cch d. Thay (2-16) vo (2-20), ta c:

r rn - 18e"*d ^TTT^T (2-21)

e + 1

Langmuir (1938) cho s n gin ho khc d nhn c in th ti mt phng gia khi gi thit l cc b mt hl kh gn nhau nn khng c mt cc anion gia chng v din th ti b mt ht l v cng. Vi cc iu kin ny, li gii ca ng c dng:

Li gii tng i n gin ny hp l so vi li gii chnh xc trong (2-19) xa yc = 1. Vi cc gi tr yc nh hn 1, c th dng phng trnh (2-21).

2.6. NHNG L c TUONG t c g i a c c h t s t

Trong mc trc, l thuyt Gouy - Chapman cp s bin i in th v s phn b on trong cc lp kp khuch tn, mc d vi hnh dng l tng. By gi s sp xp cc ht s ph thuc vo cc ht dy hay ht nhau qua cc lp kp ny nh th no. Cn lin h cc kt qu ca l thuyt Gouy - Chapman v cc lc tng tc gia cc ht. Do bn cht cc in tch b mt, cc [c khuch tn cc Lp kp l lc v. Cc lc tng tc gia hai b mt tch in trong mt cht .in phn c ih c hiu c quan h vi s tng p lc khi hai b mt c tp hp li t v cng (ti khong cch p lc bng khng) ti khong cch chia tch D. S tng p lc ph thuc vo mt ion ti mt phng gia v c cho bi nh l gi tr tip xc (Israelachvili, 1992):

P(D) = kT[pc( D ) - p c(co)] (2-23)

Trong : p (D) - p lc gia cc mt khi hai mt chia tch bi khong cch D;

PC(D) v pc(co) - cc mt ion ti mt phng gia hai b mt c chia lch tng ng bi D v v cng.

minh ho vic tnh ton p lc gia cc b mt tch in, ta hy ly trng hp cht din phn n gin 1: 1 nh NaCl. C Ih dng phng trnh (2-6) nhn c cc mt in tch quan h vi cc in th ti mt phng gia y c. Khi gi thit l in th mt phng gia bng khng khi hai b mt chia tch v tn, v xem xt c cc cation v cc anion th c th biu th phng trnh (2-23) theo:

48

P(D) - kTn0 ( e ^ /kT - l)(eCX)' /kT - 1) (2-24)

v c th xp x bng:

P ( D ) * - ^ MkT

(2-25)

Khi dng kt qu \/c t phng trnh (2-21) c gi tr khi tng tc gia cc b mt vu v cn nh l D = 2d, th c th nhn p (D) theo:

Tng lc gia hai ht thng c biu th i vi nng lng cho mi din tch n v WK, gi tr bng s ca n n thun l p lc kt hp lin quan vi D. VI th:

Nng lng y do cc lp kp khng ch l nng lng tc ng khi hai b mt tch din song song lip cn nhau. C cc lc hp dn - lc Van der Waals gia hai b mt bt k do nh hng qua li bi s chuyn ng in t ca cc nguyn t trn hai b mt. Cc in tch dao ng do cc din t chuyn ng trn qu o gy ra mmen in lc thi v to ra s hp dn gia hai b mt. i vi hai tm song song c b dy chia tch nhau khong cch 2d nng lc hp dn do cc c Van der Waals WA c biu th iheo:

Trong : A - hng s Hamaker v c gi tr 10 20J. Thng tnh gn ng WA theo cc kch thc d v 5 xc nh. Nng lng gn ng cho cc trng hp gii hn nh sau:

Tng hp cc nng lng y (2-27) v ht (2-28) khng ch s phn b' ht. Do quan h nghch vi s m ca d, cc lc hp dn Van der Waals tt nhanh khi khong cch ht tng ln. Loi nng lng khc dc gi l nng lng y Born c th hot ng khi khong cch d gim t khong ng knh mt nguyn t, n ngn chn s

(2-26)

Wr(D) - 64kTn0e

(2-27)

(2-28)

cho d (2-29)

cho d < (2-30)

WA = -----48td

cho d (2-31)

49

xm nhp vo Irong ca hai b mt. Chng ta khng quan tm n s chia tch ca loi ny l v i vi hu ht vng, s chia tch ht ch yu l nng lng y lp kp v hp dn Van der Waals.

Lc y/ht thc hot ng khi khong cch gia hai ht mang in bin i v Ihng c nh lng theo l (huyt DLVO ca Derjaguin v Landau (1941). Vcrwcy v Overbeek (1948). L thuyt ny phc ho cc giai on tng tc khc nhau gia hai ht nh thv trn s hnh 2.13.

y

tNng lng tng lc W 0

iHt

Hnh 2.13: St nng lng theo khong cch ai Nig n ng (c ht DLVO khi khong cch hai ht bin di;

b) Cc ni hihig cta l/ig c mui v th b mt hi n nng lng tng tc.

Ph thuc vo nng cht in mi v in th ca cc b mt ht. cc ht c th ht nhau ti khong cch phn tn xc nh v c th y nhau ti cc khong cch khc. Hnh 2.13a cho thy hai nh ca nng lng tng tc lng, mt pha y v mt pha ht. nh pha y ti khong cch tch bit ht l d| (trong hu ht cc h in hnh vo khong 1 - 4mm) biu hin di chn nng lng - ct ngang b mt ht b ht. ln ca nh ny quan trng cho h c cc lp khuch tn mng lin quan vi cc b mt tch in cao v cc cht in phn c nng thp, ngoi khong cch biu hin di chn nng lng, cc lc ht yu c th ln ti v dc xcm l cc lng ti thiu th sinh ( phn bit chng vi cc lng ti thiu nguyn sinh c gn b mt cc ht nhiu hn. Cc lc ny ng lu trong cc h vi h cht in phn c c dc. Kh nhiu ln, cc khong cch chia tch ht n mc di chn nng lng khng c vt qua v cc hi ht nhau bng cc lc yu tng ng vi cc lng ti thiu th sinh ny. Cc ht si thng kt bng trong dung dch st lng l do cc lc yu ny. Khi lc nh, d dng vt qua cc lc ht v cc ht c phn tn tr li.

Hnh 2.13b cho thy cc dng cong tng tc c kh nng gia cc b mt hi. Vi cc ht lng tc yu nh trong cc trng hp in th thp v nng mui cao, di

50

chn nng lng s tr nn qu yu. Vi th th vn ' on nh" ca cc ht chm bt u kt bng (t "a" sang "b"). Hon cnh c th xut hin khi nng cht in phn phi t "nng ng t gii hn" qu nng ny di chn y bin mt ("c" v "d") v cc ht bl u kt bng nhanh.

T tho lun trn hin nhin l s phn tch nh lng cc lc bn trong ht c kh nng ti phm vi xc nh khi chng ta l tng cc ht st nh l cc tm song song vi in tch be mt ca chng v cc tnh cht mi trng bit.

Trong h thc, cc lc tng tc c th khng ch do b mt ht gn nhau m cn do cc gc hl b l ra. V d, cc gc ht c th bc l cc cation v biu th cc lp kp c cha kh nhiu anion. Do vy, cc nng lng hp dn lp kcp c th chim u th gia cc gc v b mt ht trong h. C kh nng dng cng cc khi nim tng qut d trnh by trn d phn tch nh lng cc lc ny. Tuy nhin, gi mt in lch trn cc b mt v cc gc ca ht khng ng tin cy v kh nng c mt cc vt liu dnh li vi nhau bn ngoi gia cc hl lm cho cc phn tch nh th km sc thuyt phc. Vt cht hu c c mt trong h v cc vt liu xc dinh khng phi st nh oxit st, oxit nhm v cacbonat lin kl vi b mt ca mt hay nhiu ht st. Cc vt liu nv tham gia vo lin kt bng lin kt ho mnh hn hay bi cc lc Van de Waals. Cc lc lin kt o cc tc nhn gn kt ny th khng t ng gp thng qua s phn tch nh lng mc quy m ht.

iu quan trng cn bit l c mt s khc nhau gia cc h st dng dung dch st lng v khi t nguyn vn. Cc khi t him khi ch gm mt khong vl. Cc ht tng tc c th thuc v cc khong vt khc nhau v nh th c th khng tun Ih s sp xp tm song song l tng. in th ca cc ht cng bin i rt ln. S c mt cc hl bi v st c a vo bn trong hn hp ht mn c cc yu cu thm, l v cc nguyn l cht keo khng p dng cho cc ht ny, D c cc hn ch ny, cc l thuyt gii thch irn cho ta c s l thuyt phn on nh tnh tc ng ca s bin i thng s h cho n s sp xp ht v n cu trc t.

2.7. BIN I CU TRC DO c KET v n n c h t

Lc bn ngoi tc dng ln h t ht mn s chng li cc lc y gia cc ht v c xu hng lm gim khong cch trung bnh gia cc ht. Mc d c kt v nn cht u lin quan vi tc dng ca ti trng ngoi, s khc nhau quan Irng gia hai qu trnh ny c lin quan n lng nc c mt trong h. Trong trng hp c kt, th tch rng gim din ra trong iu kin bo ho. S sp xp ht trong qu trnh gim khong rng, c khi qut ho trong hnh 2.14. gim h s rng, mc nh hng cc ht st tng ln. T mt cu trc kt bng h c cc tip xc gc vi cnh ti A chuyn sang

51

dng sp xp mt vi mt ti B. Ti trng tc dng tip tc se to ra trng thi c , y ton b ht st c nh hng mt song song vi mt.

Cu hi t ra [ ti rng c ln thch hp ra sao c th tc dng n khi t khc phc hon ton cc lc y tn ti gia cc ht v dn n trng thi tip xc vt l cc ht. Do cu trc phc tp ca khi t nn kh nh gi s phn b lc t dng mu sang dng ht. nh nghin cu gin tip cc l rng b nn do ng sut c kt tng d c tin hnh bng l rng k thu ngn Griffiths v Joshi (1989) quan st cc bin i v s phn b kch c l rng ca st ti cc giai don c kt khc nhau bt u t trng thi gii hn chy. Hnh 2.15 cho thy th tch khong rng to bi cc l rng c kch c khc nhau bin i khi ng sut c kt tng ln nh ch no.

Hnh 2.14:Cc bin doi cu trc nong qu tr nil c kt

Bn kinh l ring (nm)

Hnh 2J5: Cc bin di th cl rn ttig ng cc l rng kich thc khc nhau gy ra (lo ng sut c kt (theo Griffiths v Joshi, 989)

52

Lin quan vi Irng thi gii hn chy, s tng ng sut c kt dn n s gim khong rng do cc l rng ln hn 800mm chim ch. Mc d ng sut c kt lin giam ton b khong rng, khi ng sut c kt tng (h tch khong rng o cc l rng trong nhm kch c 100 n 800mm chim ch tng ln. iu ny th hin bn cht khng gin ca l rng trong cm gic ( thc) l cc l rng ln hn (ln hn 800mm) khng sp l hon ton nhng ihay th bi s nn n l rng nh hn ( gia 100 v 800mm). v quan trng l nhm cc l rng nh hn lOOmtn. ng sut c kt hnh nh khng nh hng n nhm nv ti mc ln hn phm vi sai s ca cc thc nghim. iu ny biu hin l t nht cho ti ng sut c kt l 1500kPa, c th thy r cc l rng kch c nh hn lOOmm c th khng b nn p.

Tuy nhin, trong trng hp m cht, lng nc c mt irong h c gii hn bi lng nc t p. Nc c kh nng khng thch hp pht irin hon chnh lp kcp. Latnbe (] 958) trnh by khi nim v s sp xp ht trong qu Irnh m cht nh sau: nh thy trong hnh 2.16, m thp ti A lm cho nng cht din phn gn ht cao v to p kp dy.Lc v gia cc ht gim v do vy cc ht c xu hng kt bng. m t p tng ti B gy ra s trng n cc lp kp v do mc kt bng gim i. iu ny to ra s sp xp Irl t hn v s dnh hng cc ht vk

nh 2.16: Cc bin di cu trc trong qu tiih dm cht

(theo Larnbe, 1958

hu qu l dung trng m cht cao hn. S tng thm na m lm cho s trng n lp kp tip tc, nng cht in phn xung quanh b mt ht gim i v mc nh hng ht ln hn. Tuy nhicn, ung trng ca t gim l do cc ht dt b pha long. iu ny tng ng trng khi nhn bit c trong hnh 2.16. Lc m chl cao hn lm cho mc nh hng ht n hn v sp xp gn hn do nng lng ph thm tc ng dn h (cc trng thi D v E trong hnh 2.16).

Cc khi nim trcn do cc nh kho st tin hnh o trc tip s nh hng ht c gi tr trong phm vi gii hn (Bolt, 1955; Quigley v Thompson, 1966, Seed v Chan, 1959). Cc s liu ca Seed v Chan (1959) hnh 2.17 ph hp vi kt lun trcn l mc nh hng ht tng khi m bin di t pha kh ti pha t ca m tt nht.

53

Hnh 2.17: Sdnl hng ht ('a st m l ii hiu di khi m h lphia kh dn pha t ca m t,r nht (theo Seed v Chan, 1959)

Ni chung, s bin i trong cch sp xp hl ca t Hn quan vi cc hin i rng v phn b kch c l rng. Cc bin i v cc thng s ny nh hng trc tip cc c tnh dn cht lng ca . Garcia - Bcngochca et ill (1979) d xc nh cch phn b kch c l rng ca t st m cht bng l rng k thu ngn nhm d kin kho st cc kiu m cht tc ng n cu trc nh th no. Cc ng cong phn b kch c l rng ca hn hp 90% bi v 10% kaolin c m cht bng lc m cht cao nhn c t cc nghin cu ca ho. dc thv trong hnh 2.18. T cc ng cong nv r rng l hai nhm ] rng khc nhau tn ti, mi nhm gia 10(.un v J[j.m (c xcm l kicu l rng ln) v

ng knh l rng gii han (um)

Hnh 2.18: Cc cii cong phn bo kch c r) t khi II ha II cho 90% bi v 10% kaolin

dc H ch! H ini lc dm c cao

(theo Grcia Bengtchea et a!, 979)

54

mi nhm khc tp trng khong 0,1 fim (c xem l kiu l rng nh). uan st ny c hiu lc nhm l rng c gia cu trc vi m v kin c nh, hoc gia cm v Irong cm. C th thv trong hnh 2.18 l kiu l rng nh th tng i nh nhau tt c trng thi m cht, kiu l rng ln v (r v khong cch dng nh thay i theo m chl. Garcia - Bengochea et al (1979) nhn nh l ni chung, v tr v khong cch ca kiu l rng ln l cc chi s' tt nht cho s bin i cu trc t do m v [c dm cht bin i i vi mt loi t cho. Cng d xc nh l kiu l rng ln khng ch bn cht dn cht lng ca t. Do vy, s bin cu trc t phi l mt xem xct quan trng trong nghin cu bat k no c lin quan vi s phn v s vn chuyn cc cht nhim trong t uc m ch.

2.X. VAI TR CA CU TRC DAT EN h n h VI K THUT CA T

Cu trc t trn c s nh hng ca n n s phn b kch c l rng, dng vai tr quyt nh n cc tnh cht dn cht lng ca t. N cng khng ch s n dnh ca mng l rng. Cc ht kch c kco mn c th c tch ra t mng nguyn vn lng di d v c huy ng trong dng l rng c cc lin quan quan trng n s phn v s vn chuyn cc cht nhim. Cc ht sl c din tch b mt cao v hp ph lng cht nhim ln. Tnh di dng ca chng m ch s di ng ca cc cht nhim kt giao v do vy bin di kh nng vn chuyn cht nhim di mt dt. Qu trinh nv c gi l vn chuycn c Ihun tin (d dng) v c ch nhiu trong cc thp nin gn y.

lnh 2.19

Cu trc t cng ng vai tr quyt nh trong hnh vi k thut v c hc ca t. Cc k s a k thut quan tm ch yu n cu trc t nh hng ti bn ca l nh th' no. Tn tht bn khi t st nguyn dng c c li thng bieu hin bng

nhv cm ca t (t s bn l nguvn dng vi t ch b), c cu trc t khng ch irong phm vi rng. Quan h ng sut - bin dng ca t sl nhv cm c thy trn hnh 2.19. Kt cu t st nguyn dng in hnh bao gm cc t hp kt bng h chu bin dng thp din ra s ph v ca mt s' lin kt bn trong. Sau t st mt ht bn ti trng thi ging ht trng thi to ra do (ch b) t din ra khi cc lin kt cu trc ban u b ph v.

Nhm t st khc bit l t st phn tn biu hin bn cht xi mn cao l do s n nh ca cu trc t. Khi c phn trm kali cao trong lp hp ph, t tr ncn d chu nh hng phn tn cc ht (c thi, ngay c khi khng c dng cht lng l rng. l s khc nhau c bn vi hin tng xi mn ht c th xy ra khi gradien thu lc qu ln. Hai thut ng dc bit h s hp ph natri (SAR - sodium adsorption ratio) v phn irm natri c th Irao di (ESP - exchangeable sodium percentage) c dng nh cc chi bo v bn chl phn tn ca t st. Chng c nh ngha l:

SAR(mEq/l) 1/2 Na"1[(Ca2+ + M g ^ )/2 ]U2 + '

(2-32)

ESP: (N a1) T -kh nng Irao i tong

(2-33)

Cc nng trong SAR cp ti dung dch l rng, trong khi nng natri Irong ESP cp li phc hp Irao i ca t. Ni chung, t c ESP ln hn 2% c xem c kh nng phn ln. Sherard et al (1976) bng mt s cc quan st thc nghim c nhn c ticu chun cho s phn tn t (hnh 2.20). Ba vng c nhn ra: vnti A, c th hi vng c phn tn; vng B - phn tn dng nh khng xy ra; v vng trung giun C: t c th phn tn hoc khng.

-f U ^ I I I I I ~-L _ L I p f w ] r~ rp

: 54? ; ? r,1) nghin cu u n v c thv trong hnh 3.7. Hnh ny cho bit l, ni ch un t s gim l hai n ba ln thm khi cu trc t chuvn t pha kh n pha t ca am tt nht. Tnh thm thp nhi xy ra pha t ciia m li nh. khi virt qu c kh nng hi phc phn no. l c s cho quv trinh k thut hin thi khi chun hi dai st m cht pha t cua m tt nht trong khi xy dng lp set lt cho bi cha cht thi. Tnh thm trong hnh 3.7 tng ng trng thi bo ho vi bo ho t c t trng thi ch b ban du. th v li C cng s liu hnh 3.8 cho Ihy s tng phn manh gia ct v t st m cht 111 tnh thm ca l st dm chl khng ch ph thuc duv nht vo dung trng kh (hay h s rn2 ). Vi d rn ch h l 9% kh nng thm thav di hu nh ba bc v n, mc d ung irna kh l hng s. Cc nghin cu gn v d xc lp CLC nh huiL' ca cc bin nh loi v nng lng m cht v kch c cc cc t dng trona qu trnh m cht. C cc

70

phng php dm cht ngoi tri khc nhuu: m nn. m nn lnh, m ncn bng nho trn v dam rune. Phng php m chp nhn c nh hng ln n kt cu v kh nng thm ca st m cht. Ngi c c the tham kho s m t chi tit cc vn ny ca Dav v Daniel (1985) v Daniel (1987). Theo m hnh chm ca Olsen c th hiu nh hng ca cc kch c cc t n tnh thm (hnh 2.5).

nh 3 .7:Bin i h s thm theo m t ch'b I' nng lng dm cht theo Milcicl c a. 1965)

"14

2-s

1 X1Q

nh 3.8: I 2S kiii nrng \K'/ 1 X 1 0 7

j 1 X oV i t a dim if t r o i i k l 6

4 h i l i i h s' ro i l ) 2nh l ch bo v !)1 1 10 J

k h i t i i q l i i i i t r v i i n i i l p 6

i s! ilni chi( t c o M i t c i t e l l C I d . 1 9 6 5 )

1 x 1096 100 104 108 112 116 120

Dung trang kh

71

S gim kch thc cuc dl v loi Ir cc l rng gia cc cc s cho cc l rng vi kt cu nh hn v dn n kh nng thm nh hn. iu ny c Bcnson v Daniel (1990) xc nhn bng thc nghim.

Khng ging trng hp ca ct. ho hoc ca s thm thu (ngoi tnh ch vt t ca nht) nh hng tnh (hm t st m cht. l do ho b mt m cc ht st biu hin khi tng tc vi cht [ng l rng trong giai oan ch b cng nh trong giai on thm. L Ihuyt lp kp khuch tn cp trong chng 2 cho c s rt ra cc kl un tng qut v ho thm [hu bin i vi cu trc ca t st m chl nh th no. Da (rcn s thm thu dang xc tin cu trc kct hng hay phn tn. t nht c kh nng phng on nh tnh nh hng cn tnh llm. Cc yu t' lm im b dy lp kp hav chiu di Debye [1/K. y K biu th bng phng trnh (2-10)1. lo ra kt cu k bng trong khi c th ni lng kt cu phn tn. Ni chung, kt cu kt bng lm tng tnh thm cn kt cu phn tn lm gim lnh ihm. Da trn cc nh hng ca thanh phn cht lng l rng n b dy lp kp khuch tn, c th phng on cc bin i ging nh Ihc v tnh thm. Xu hng bin di tnh thm do s bin i cc ting s cht lng l rng ph bin c thy trong bng 3.1. Nehin cu thc nghim ca Mitchcll v Madsen (1987), d khng nh xu hng nh tnh thy trong hng .1.1. Tuy nhin, nhicu nh khao st hn ch cho cc lOi chl tinh khit v ih gian Ih nghim thm l ngn. Cc nh hng ca mt s cht nhim thc, a dng n cu trc t v k cha c tbil lp v cc vn e nv s l phm vi nghcn cu si ng cn c tip tc trong k thut a mi trng.

Bang 3.1. Cc xu hng bin oi tnh thm do tng cao cc thng s cht lng l rng ph bin

Cc thng s dc lang

Xu hng b ily lp kp khuch tn ( 1/K)

Cu trc t to ra

X hng lnh (hm

pH Tng Phn tn (irn

Nng d chl din phn Gim Kt bng Tng

1 lo tr cation Gim Kt bng Tng

Kch thirc caon Tng Phn tn Giam

Hng s cht in mi Tng Phn tn Gim. .

Mt s' phng php th nghim trong phng anii c dng o c khii nn? thm cua t st m cht. Su cn thit xc nh ehnli xc thm d khin cho cc phng php th nghim pht trin mt cch rt nhanh. N c c th tham khao Daniel (1994) v vic x l theo su ca cc phng php th nghim c kh nng xc nh k ca t st m cht tron phng khc nhau. Ni chung, cc phng php (hc nghim dc phn ihnh hai nhm ln da trn ihit b s dung thm k thnh cng v

72

thm k thnh mm. Mc d pht hin rng hai phng php ny kh nht tr nhau (Routwell v Rauser. 1990, Daniel, 1994), s thm k lin quan vic chun b mu v cc khc nhau irong s chun b trong phng v ngot tri lo ra s khng tin cv ln Irng khi xc nh k. Daniel (1989) cho thv kh nng thm hin trnc thng ln hn 10 n 1000 ln bng cc phng php trong phng. V th vic xc nh chnh xc k ca t sl m chl vn cn l mt thch thc ln i vi cc k s a mi trng.

3.3. PHNG TRNH CHI O DNG THAM b o HO

Ta tin hnh dng nh lut Darcy v khi nim thm pht trin mt phng trinh ton hc ch o qu trnh thm bo ho. Chng la tm kim bicu thc tng qut khng ch qu trnh trong dng thm c bn c dng cho bt k v di nhm bt k cc diu kin bin v ban u cho. Kh chng ta tin hnh vi cc qu trnh tng t chng la vin dn nh lut lng quan bo ton khi lng '' kt hp n vi quan h nguvn nhn v hu qu, Irong trng hp ny t nh lut Darcy. Ngi c c (h quan st song hnh gia hin tng ny v cc qu trnh khc trong c hoc cht rn (ni cn bng lc c kct hp vi nh lut Hookc), trong dn nhit (ni s bo tn nng lng c kt hp vi nh Lut dn nhit)...

z (pV; ) z

PV r-fpvjtSx

Hnh 3.9: Bo ton k ltt troiu> th lch inyn t m st

Chng la s dng nguvn bo ton khi ing cho ml the tch nguyn t gim st dc Ihy Irong hnh 3.9. Tham kho th tch nv, nguyn l pht biu :

Lu lng bin i = tr trong th tch (3-30)

nguvn t gim st

Lu lng khi ra

Lu lng khi vo

73

Khi bicu th bng ton hc theo ba hng, VC trii ca phng tnh (3-30) Ir thnh:

pV, - ~ ( p v x ) - pVx + pV - (pvs ) - pV + pv z - ( p v , )ox j _ ay ' J [_ C7

-p V ,

havx

Trong d: p - dung ng chi lng;

v x. Vv v Vz - cc vn tc dng thm llico cc hng X, y v z.

!r trong th tch nguyn t quan st bin i do dung trng cht lng thav i gy ra s dn n hav co ngt cht lng hoc do th lch l rne ca nguycn t thav i. S thay i SU1 l do kh nng p co ca t ph thuc vo thi gian. Vi cc t hi mn, l qu trnh c kt kh quen thuc vi cc k s a k ihut. Khi nh gi hai ycu lo nv v phi phng trnh (3-30), nguyn l ho ton khi lng c th biu din dng:

^ - t p v , ) - - ^ ( p v ) - - ^ ( p V , ) = - H p n )OX v 07. t

(3-3 I )

Tc bin di (r thng dc biu (h theo thng s tr ring S4 - th tch nc m mt ch lch n v tng cha nc phng thch khi tr di dc CInuc thu lc ] n v. Thng s nv c th bicu ih bao trm cc nh hng ca lnhp co ca ch lng v mi trng theo dng (xem Freeze v Cherrv, 1979):

S4= p g (a + nP) (3-32)

Trong :

a - h s' nn ca mi trng l rng, c nh ngha l s bin di (hc tch dl cho mi bin di dn v ng sut hiu qu;

p - h s nn ca cht lns khi bin i th tch cht lng cho mi bin i dn v p lc nc [ rng . V th

-dV T /VTt =

va | =

d a

-dV w/Vwdu

(3-33)

(3-34)

pht hin l, phng irnh (3-33) cho s tip ni gia phng trnh dng ihni bio ho vk phnu trnh c kt ca Tcrzaghi.

Biu din theo tr rint, nguvn l bo ton khi lng phdg trnh (3-3 )J c Ihc vit li dns:

- ( P v x ) - - (pV,.) - 1 (pV /) = p Ss ^< X < \ ' V'f. ( I! X c* \

Tron : h - CI nc thu lnh.

(3-35)

74

By gi ta kt hp nh iut Darcy vit cc thnh phn vn tc vi cc (h p lc c biu hin theo ct nuc tliuv (nh h:

Trong : kx. ky v kz - h s thm theo cc hng X . V v I. ng ng; trong phng trnh (3-36) loi tr p VI s bin i cc thnh phn vn c ln hn nhiu s bin i p theo to khng gian. iu nv ch php loi b cc thnh phn Vx(p/5x), Vv(dp/c?v) \' V/{c?p/cv.) khi v ri dc m rng bng nguyn tc chui. Khi ai thit mi trng bo ho l dng nht v ng hng (kH = kv = kz = k), c Ih n gin ho phng irnh (3 -3 6 )Ihnh:

Hu ht cc vn hnh m hnh dng nc di t lin quan cht ch vi vic gii , phng trnh (3-37) trong hnh ihc nv hoc hnh thc khc cho mt phm vi quan tm

ling. Khi tn ti cc li gii dng ng cho cc trng hp ring xc nh, ni chung cn cc phng php s. Chng ta s tho lun di y mt s trng hp ring e nhn c s hiu bit su sc v cc bi ton cho dng